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 $145.74   4.759%   $152.6758   $152.68   $152.70   $152.70  
  Purchase #2 $207.63   4.530%   $217.0356   $217.04   $217.05   $217.00  
  Purchase #3 $65.93   3.752%   $68.4037   $68.40   $68.40   $68.40  
  Purchase #4 $173.65   12.138%   $194.7276   $194.73   $194.75   $194.70  
  Purchase #5 $115.27   4.792%   $120.7937   $120.79   $120.80   $120.80  
  Purchase #6 $33.55   11.653%   $37.4596   $37.46   $37.45   $37.50  
  Purchase #7 $201.75   11.137%   $224.2189   $224.22   $224.20   $224.20  
  7 purchase totals = $943.52       $1,015.3149   $1,015.32   $1,015.35   $1,015.30