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 $238.47   8.467%   $258.6613   $258.66   $258.65   $258.70  
  Purchase #2 $86.85   9.332%   $94.9548   $94.95   $94.95   $95.00  
  Purchase #3 $162.86   7.424%   $174.9507   $174.95   $174.95   $175.00  
  Purchase #4 $245.50   3.830%   $254.9027   $254.90   $254.90   $254.90  
  Purchase #5 $220.79   5.610%   $233.1763   $233.18   $233.20   $233.20  
  Purchase #6 $27.32   7.843%   $29.4627   $29.46   $29.45   $29.50  
  Purchase #7 $10.29   3.531%   $10.6533   $10.65   $10.65   $10.70  
  7 purchase totals = $992.08       $1,056.7618   $1,056.75   $1,056.75   $1,057.00