Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $187.44   11.326%   $208.6695   $208.67   $208.65   $208.70  
  Purchase #2 $180.56   3.459%   $186.8056   $186.81   $186.80   $186.80  
  Purchase #3 $236.52   4.214%   $246.487   $246.49   $246.50   $246.50  
  Purchase #4 $105.88   6.823%   $113.1042   $113.10   $113.10   $113.10  
  Purchase #5 $170.40   4.105%   $177.3949   $177.39   $177.40   $177.40  
  Purchase #6 $238.73   6.161%   $253.4382   $253.44   $253.45   $253.40  
  Purchase #7 $163.65   3.862%   $169.9702   $169.97   $169.95   $170.00  
  7 purchase totals = $1,283.18       $1,355.8696   $1,355.87   $1,355.85   $1,355.90