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 $14.86   12.207%   $16.674   $16.67   $16.65   $16.70  
  Purchase #2 $169.55   3.819%   $176.0251   $176.03   $176.05   $176.00  
  Purchase #3 $158.36   11.187%   $176.0757   $176.08   $176.10   $176.10  
  Purchase #4 $245.73   12.359%   $276.0998   $276.10   $276.10   $276.10  
  Purchase #5 $106.73   11.518%   $119.0232   $119.02   $119.00   $119.00  
  Purchase #6 $54.32   7.170%   $58.2147   $58.21   $58.20   $58.20  
  Purchase #7 $43.94   7.153%   $47.083   $47.08   $47.10   $47.10  
  7 purchase totals = $793.49       $869.1955   $869.19   $869.20   $869.20