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 $228.48   11.418%   $254.5678   $254.57   $254.55   $254.60  
  Purchase #2 $182.33   5.653%   $192.6371   $192.64   $192.65   $192.60  
  Purchase #3 $41.44   8.631%   $45.0167   $45.02   $45.00   $45.00  
  Purchase #4 $29.66   8.726%   $32.2481   $32.25   $32.25   $32.20  
  Purchase #5 $59.41   7.139%   $63.6513   $63.65   $63.65   $63.70  
  Purchase #6 $158.35   13.739%   $180.1057   $180.11   $180.10   $180.10  
  Purchase #7 $76.68   7.648%   $82.5445   $82.54   $82.55   $82.50  
  7 purchase totals = $776.35       $850.7712   $850.78   $850.75   $850.70