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 $142.76   8.211%   $154.482   $154.48   $154.50   $154.50  
  Purchase #2 $232.87   8.767%   $253.2857   $253.29   $253.30   $253.30  
  Purchase #3 $53.28   9.142%   $58.1509   $58.15   $58.15   $58.20  
  Purchase #4 $229.80   11.192%   $255.5192   $255.52   $255.50   $255.50  
  Purchase #5 $213.54   9.720%   $234.2961   $234.30   $234.30   $234.30  
  Purchase #6 $218.57   8.791%   $237.7845   $237.78   $237.80   $237.80  
  Purchase #7 $27.33   6.111%   $29.0001   $29.00   $29.00   $29.00  
  7 purchase totals = $1,118.15       $1,222.5185   $1,222.52   $1,222.55   $1,222.60