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 $61.26   10.635%   $67.775   $67.78   $67.80   $67.80  
  Purchase #2 $204.67   6.533%   $218.0411   $218.04   $218.05   $218.00  
  Purchase #3 $25.54   4.865%   $26.7825   $26.78   $26.80   $26.80  
  Purchase #4 $238.86   6.546%   $254.4958   $254.50   $254.50   $254.50  
  Purchase #5 $19.58   11.625%   $21.8562   $21.86   $21.85   $21.90  
  Purchase #6 $43.55   9.541%   $47.7051   $47.71   $47.70   $47.70  
  Purchase #7 $243.71   6.813%   $260.314   $260.31   $260.30   $260.30  
  7 purchase totals = $837.17       $896.9697   $896.98   $897.00   $897.00