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 $200.82   11.644%   $224.2035   $224.20   $224.20   $224.20  
  Purchase #2 $70.66   8.226%   $76.4725   $76.47   $76.45   $76.50  
  Purchase #3 $143.46   8.471%   $155.6125   $155.61   $155.60   $155.60  
  Purchase #4 $107.37   5.563%   $113.343   $113.34   $113.35   $113.30  
  Purchase #5 $82.46   10.807%   $91.3715   $91.37   $91.35   $91.40  
  Purchase #6 $195.35   12.148%   $219.0811   $219.08   $219.10   $219.10  
  Purchase #7 $168.90   3.157%   $174.2322   $174.23   $174.25   $174.20  
  7 purchase totals = $969.02       $1,054.3163   $1,054.30   $1,054.30   $1,054.30