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 $29.26   6.704%   $31.2216   $31.22   $31.20   $31.20  
  Purchase #2 $220.71   13.405%   $250.2962   $250.30   $250.30   $250.30  
  Purchase #3 $31.60   6.792%   $33.7463   $33.75   $33.75   $33.70  
  Purchase #4 $32.76   10.155%   $36.0868   $36.09   $36.10   $36.10  
  Purchase #5 $209.44   9.664%   $229.6803   $229.68   $229.70   $229.70  
  Purchase #6 $168.90   12.679%   $190.3148   $190.31   $190.30   $190.30  
  Purchase #7 $234.64   8.617%   $254.8589   $254.86   $254.85   $254.90  
  7 purchase totals = $927.31       $1,026.2049   $1,026.21   $1,026.20   $1,026.20