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 $176.62   11.783%   $197.4311   $197.43   $197.45   $197.40  
  Purchase #2 $204.49   3.820%   $212.3015   $212.30   $212.30   $212.30  
  Purchase #3 $246.90   7.556%   $265.5558   $265.56   $265.55   $265.60  
  Purchase #4 $44.39   11.551%   $49.5175   $49.52   $49.50   $49.50  
  Purchase #5 $65.64   5.407%   $69.1892   $69.19   $69.20   $69.20  
  Purchase #6 $54.51   8.130%   $58.9417   $58.94   $58.95   $58.90  
  Purchase #7 $100.98   3.439%   $104.4527   $104.45   $104.45   $104.50  
  7 purchase totals = $893.53       $957.3895   $957.39   $957.40   $957.40