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 $212.92   13.496%   $241.6557   $241.66   $241.65   $241.70  
  Purchase #2 $96.71   3.269%   $99.8714   $99.87   $99.85   $99.90  
  Purchase #3 $147.84   6.147%   $156.9277   $156.93   $156.95   $156.90  
  Purchase #4 $26.69   8.874%   $29.0585   $29.06   $29.05   $29.10  
  Purchase #5 $117.29   6.398%   $124.7942   $124.79   $124.80   $124.80  
  Purchase #6 $159.32   10.256%   $175.6599   $175.66   $175.65   $175.70  
  Purchase #7 $171.96   4.208%   $179.1961   $179.20   $179.20   $179.20  
  7 purchase totals = $932.73       $1,007.1635   $1,007.17   $1,007.15   $1,007.30