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 $245.31   5.522%   $258.856   $258.86   $258.85   $258.90  
  Purchase #2 $51.84   5.495%   $54.6886   $54.69   $54.70   $54.70  
  Purchase #3 $193.61   5.623%   $204.4967   $204.50   $204.50   $204.50  
  Purchase #4 $60.45   13.339%   $68.5134   $68.51   $68.50   $68.50  
  Purchase #5 $6.54   5.811%   $6.92   $6.92   $6.90   $6.90  
  Purchase #6 $75.28   4.324%   $78.5351   $78.54   $78.55   $78.50  
  Purchase #7 $148.31   8.113%   $160.3424   $160.34   $160.35   $160.30  
  7 purchase totals = $781.34       $832.3522   $832.36   $832.35   $832.30