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 $57.50   9.171%   $62.7733   $62.77   $62.75   $62.80  
  Purchase #2 $115.72   10.570%   $127.9516   $127.95   $127.95   $128.00  
  Purchase #3 $194.37   11.136%   $216.015   $216.02   $216.00   $216.00  
  Purchase #4 $75.82   9.455%   $82.9888   $82.99   $83.00   $83.00  
  Purchase #5 $241.39   5.136%   $253.7878   $253.79   $253.80   $253.80  
  Purchase #6 $152.58   9.390%   $166.9073   $166.91   $166.90   $166.90  
  Purchase #7 $102.30   10.155%   $112.6886   $112.69   $112.70   $112.70  
  7 purchase totals = $939.68       $1,023.1124   $1,023.12   $1,023.10   $1,023.20