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 $62.80   6.650%   $66.9762   $66.98   $67.00   $67.00  
  Purchase #2 $120.84   11.872%   $135.1861   $135.19   $135.20   $135.20  
  Purchase #3 $175.74   13.311%   $199.1328   $199.13   $199.15   $199.10  
  Purchase #4 $14.86   6.453%   $15.8189   $15.82   $15.80   $15.80  
  Purchase #5 $150.37   3.367%   $155.433   $155.43   $155.45   $155.40  
  Purchase #6 $85.60   6.102%   $90.8233   $90.82   $90.80   $90.80  
  Purchase #7 $124.62   6.339%   $132.5197   $132.52   $132.50   $132.50  
  7 purchase totals = $734.83       $795.8900   $795.89   $795.90   $795.80