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 $146.47   5.660%   $154.7602   $154.76   $154.75   $154.80  
  Purchase #2 $24.74   5.138%   $26.0111   $26.01   $26.00   $26.00  
  Purchase #3 $55.88   8.782%   $60.7874   $60.79   $60.80   $60.80  
  Purchase #4 $131.38   7.842%   $141.6828   $141.68   $141.70   $141.70  
  Purchase #5 $184.91   6.362%   $196.674   $196.67   $196.65   $196.70  
  Purchase #6 $9.82   10.532%   $10.8542   $10.85   $10.85   $10.90  
  Purchase #7 $80.83   4.690%   $84.6209   $84.62   $84.60   $84.60  
  7 purchase totals = $634.03       $675.3906   $675.38   $675.35   $675.50