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 $82.71   11.547%   $92.2605   $92.26   $92.25   $92.30  
  Purchase #2 $220.50   9.814%   $242.1399   $242.14   $242.15   $242.10  
  Purchase #3 $95.68   10.213%   $105.4518   $105.45   $105.45   $105.50  
  Purchase #4 $218.94   11.378%   $243.851   $243.85   $243.85   $243.90  
  Purchase #5 $45.32   11.255%   $50.4208   $50.42   $50.40   $50.40  
  Purchase #6 $161.63   7.404%   $173.5971   $173.60   $173.60   $173.60  
  Purchase #7 $84.85   3.190%   $87.5567   $87.56   $87.55   $87.60  
  7 purchase totals = $909.63       $995.2778   $995.28   $995.25   $995.40