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 $231.84   11.283%   $257.9985   $258.00   $258.00   $258.00  
  Purchase #2 $201.66   6.741%   $215.2539   $215.25   $215.25   $215.30  
  Purchase #3 $164.40   6.313%   $174.7786   $174.78   $174.80   $174.80  
  Purchase #4 $141.45   8.122%   $152.9386   $152.94   $152.95   $152.90  
  Purchase #5 $105.77   9.550%   $115.871   $115.87   $115.85   $115.90  
  Purchase #6 $43.66   5.780%   $46.1835   $46.18   $46.20   $46.20  
  Purchase #7 $54.63   12.244%   $61.3189   $61.32   $61.30   $61.30  
  7 purchase totals = $943.41       $1,024.3430   $1,024.34   $1,024.35   $1,024.40