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 $243.33   7.644%   $261.9301   $261.93   $261.95   $261.90  
  Purchase #2 $183.57   6.316%   $195.1643   $195.16   $195.15   $195.20  
  Purchase #3 $150.66   13.860%   $171.5415   $171.54   $171.55   $171.50  
  Purchase #4 $233.52   8.322%   $252.9535   $252.95   $252.95   $253.00  
  Purchase #5 $87.85   7.621%   $94.545   $94.55   $94.55   $94.50  
  Purchase #6 $241.49   8.416%   $261.8138   $261.81   $261.80   $261.80  
  Purchase #7 $28.61   13.121%   $32.3639   $32.36   $32.35   $32.40  
  7 purchase totals = $1,169.03       $1,270.3121   $1,270.30   $1,270.30   $1,270.30