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 $236.71   10.781%   $262.2297   $262.23   $262.25   $262.20  
  Purchase #2 $47.79   10.179%   $52.6545   $52.65   $52.65   $52.70  
  Purchase #3 $163.46   6.412%   $173.9411   $173.94   $173.95   $173.90  
  Purchase #4 $105.53   11.144%   $117.2903   $117.29   $117.30   $117.30  
  Purchase #5 $161.68   5.631%   $170.7842   $170.78   $170.80   $170.80  
  Purchase #6 $193.54   8.637%   $210.256   $210.26   $210.25   $210.30  
  Purchase #7 $147.58   10.582%   $163.1969   $163.20   $163.20   $163.20  
  7 purchase totals = $1,056.29       $1,150.3527   $1,150.35   $1,150.40   $1,150.40