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 $124.54   7.574%   $133.9727   $133.97   $133.95   $134.00  
  Purchase #2 $204.46   6.316%   $217.3737   $217.37   $217.35   $217.40  
  Purchase #3 $223.85   8.430%   $242.7206   $242.72   $242.70   $242.70  
  Purchase #4 $72.35   10.695%   $80.0878   $80.09   $80.10   $80.10  
  Purchase #5 $21.53   11.651%   $24.0385   $24.04   $24.05   $24.00  
  Purchase #6 $125.38   7.542%   $134.8362   $134.84   $134.85   $134.80  
  Purchase #7 $194.93   9.417%   $213.2866   $213.29   $213.30   $213.30  
  7 purchase totals = $967.04       $1,046.3161   $1,046.32   $1,046.30   $1,046.30