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 $228.26   13.368%   $258.7738   $258.77   $258.75   $258.80  
  Purchase #2 $77.42   5.499%   $81.6773   $81.68   $81.70   $81.70  
  Purchase #3 $204.43   11.195%   $227.3159   $227.32   $227.30   $227.30  
  Purchase #4 $236.87   11.844%   $264.9249   $264.92   $264.90   $264.90  
  Purchase #5 $65.54   5.119%   $68.895   $68.90   $68.90   $68.90  
  Purchase #6 $68.34   5.353%   $71.9982   $72.00   $72.00   $72.00  
  Purchase #7 $132.85   12.220%   $149.0843   $149.08   $149.10   $149.10  
  7 purchase totals = $1,013.71       $1,122.6694   $1,122.67   $1,122.65   $1,122.70