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 $91.52   11.224%   $101.7922   $101.79   $101.80   $101.80  
  Purchase #2 $203.38   11.428%   $226.6223   $226.62   $226.60   $226.60  
  Purchase #3 $168.86   12.174%   $189.417   $189.42   $189.40   $189.40  
  Purchase #4 $218.59   7.392%   $234.7482   $234.75   $234.75   $234.70  
  Purchase #5 $49.87   3.153%   $51.4424   $51.44   $51.45   $51.40  
  Purchase #6 $201.84   5.140%   $212.2146   $212.21   $212.20   $212.20  
  Purchase #7 $110.31   4.347%   $115.1052   $115.11   $115.10   $115.10  
  7 purchase totals = $1,044.37       $1,131.3419   $1,131.34   $1,131.30   $1,131.20