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 $228.40   8.113%   $246.9301   $246.93   $246.95   $246.90  
  Purchase #2 $92.96   12.538%   $104.6153   $104.62   $104.60   $104.60  
  Purchase #3 $9.28   5.223%   $9.7647   $9.76   $9.75   $9.80  
  Purchase #4 $47.82   6.569%   $50.9613   $50.96   $50.95   $51.00  
  Purchase #5 $99.85   7.449%   $107.2878   $107.29   $107.30   $107.30  
  Purchase #6 $57.80   12.178%   $64.8389   $64.84   $64.85   $64.80  
  Purchase #7 $247.59   5.268%   $260.633   $260.63   $260.65   $260.60  
  7 purchase totals = $783.70       $845.0311   $845.03   $845.05   $845.00