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 $111.50   7.162%   $119.4856   $119.49   $119.50   $119.50  
  Purchase #2 $16.92   12.648%   $19.06   $19.06   $19.05   $19.10  
  Purchase #3 $66.53   5.764%   $70.3648   $70.36   $70.35   $70.40  
  Purchase #4 $33.92   8.573%   $36.828   $36.83   $36.85   $36.80  
  Purchase #5 $95.53   7.129%   $102.3403   $102.34   $102.35   $102.30  
  Purchase #6 $114.47   9.740%   $125.6194   $125.62   $125.60   $125.60  
  Purchase #7 $114.54   6.702%   $122.2165   $122.22   $122.20   $122.20  
  7 purchase totals = $553.41       $595.9146   $595.92   $595.90   $595.90