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 $57.84   6.404%   $61.5441   $61.54   $61.55   $61.50  
  Purchase #2 $32.73   4.814%   $34.3056   $34.31   $34.30   $34.30  
  Purchase #3 $80.90   6.298%   $85.9951   $86.00   $86.00   $86.00  
  Purchase #4 $216.46   3.461%   $223.9517   $223.95   $223.95   $224.00  
  Purchase #5 $13.87   9.502%   $15.1879   $15.19   $15.20   $15.20  
  Purchase #6 $63.61   6.778%   $67.9215   $67.92   $67.90   $67.90  
  Purchase #7 $243.75   3.648%   $252.642   $252.64   $252.65   $252.60  
  7 purchase totals = $709.16       $741.5479   $741.55   $741.55   $741.50