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 $211.79   10.727%   $234.5087   $234.51   $234.50   $234.50  
  Purchase #2 $171.78   8.767%   $186.84   $186.84   $186.85   $186.80  
  Purchase #3 $41.35   7.443%   $44.4277   $44.43   $44.45   $44.40  
  Purchase #4 $61.86   13.197%   $70.0237   $70.02   $70.00   $70.00  
  Purchase #5 $119.84   3.809%   $124.4047   $124.40   $124.40   $124.40  
  Purchase #6 $202.35   7.256%   $217.0325   $217.03   $217.05   $217.00  
  Purchase #7 $49.45   6.437%   $52.6331   $52.63   $52.65   $52.60  
  7 purchase totals = $858.42       $929.8704   $929.86   $929.90   $929.70