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 $150.82   11.781%   $168.5881   $168.59   $168.60   $168.60  
  Purchase #2 $75.42   12.576%   $84.9048   $84.90   $84.90   $84.90  
  Purchase #3 $122.54   6.589%   $130.6142   $130.61   $130.60   $130.60  
  Purchase #4 $236.87   13.359%   $268.5135   $268.51   $268.50   $268.50  
  Purchase #5 $151.62   7.571%   $163.0992   $163.10   $163.10   $163.10  
  Purchase #6 $154.96   3.510%   $160.3991   $160.40   $160.40   $160.40  
  Purchase #7 $120.84   5.280%   $127.2204   $127.22   $127.20   $127.20  
  7 purchase totals = $1,013.07       $1,103.3393   $1,103.33   $1,103.30   $1,103.30