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 $207.50   8.522%   $225.1832   $225.18   $225.20   $225.20  
  Purchase #2 $74.67   13.111%   $84.46   $84.46   $84.45   $84.50  
  Purchase #3 $157.31   6.784%   $167.9819   $167.98   $168.00   $168.00  
  Purchase #4 $57.71   11.861%   $64.555   $64.56   $64.55   $64.60  
  Purchase #5 $164.38   7.658%   $176.9682   $176.97   $176.95   $177.00  
  Purchase #6 $210.85   9.494%   $230.8681   $230.87   $230.85   $230.90  
  Purchase #7 $49.76   8.208%   $53.8443   $53.84   $53.85   $53.80  
  7 purchase totals = $922.18       $1,003.8607   $1,003.86   $1,003.85   $1,004.00