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 $53.57   7.339%   $57.5015   $57.50   $57.50   $57.50  
  Purchase #2 $92.88   11.796%   $103.8361   $103.84   $103.85   $103.80  
  Purchase #3 $204.28   12.532%   $229.8804   $229.88   $229.90   $229.90  
  Purchase #4 $194.75   3.313%   $201.2021   $201.20   $201.20   $201.20  
  Purchase #5 $211.76   10.401%   $233.7852   $233.79   $233.80   $233.80  
  Purchase #6 $100.85   3.205%   $104.0822   $104.08   $104.10   $104.10  
  Purchase #7 $83.33   11.197%   $92.6605   $92.66   $92.65   $92.70  
  7 purchase totals = $941.42       $1,022.9480   $1,022.95   $1,023.00   $1,023.00