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 $95.39   8.224%   $103.2349   $103.23   $103.25   $103.20  
  Purchase #2 $84.55   8.619%   $91.8374   $91.84   $91.85   $91.80  
  Purchase #3 $61.53   5.247%   $64.7585   $64.76   $64.75   $64.80  
  Purchase #4 $161.52   3.341%   $166.9164   $166.92   $166.90   $166.90  
  Purchase #5 $152.40   8.325%   $165.0873   $165.09   $165.10   $165.10  
  Purchase #6 $80.85   9.450%   $88.4903   $88.49   $88.50   $88.50  
  Purchase #7 $220.71   7.124%   $236.4334   $236.43   $236.45   $236.40  
  7 purchase totals = $856.95       $916.7582   $916.76   $916.80   $916.70