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 $24.45   8.367%   $26.4957   $26.50   $26.50   $26.50  
  Purchase #2 $141.51   6.384%   $150.544   $150.54   $150.55   $150.50  
  Purchase #3 $65.67   9.715%   $72.0498   $72.05   $72.05   $72.00  
  Purchase #4 $211.97   11.225%   $235.7636   $235.76   $235.75   $235.80  
  Purchase #5 $75.74   13.428%   $85.9104   $85.91   $85.90   $85.90  
  Purchase #6 $140.86   3.421%   $145.6788   $145.68   $145.70   $145.70  
  Purchase #7 $60.80   8.838%   $66.1735   $66.17   $66.15   $66.20  
  7 purchase totals = $721.00       $782.6158   $782.61   $782.60   $782.60