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 $92.53   4.455%   $96.6522   $96.65   $96.65   $96.70  
  Purchase #2 $175.92   8.784%   $191.3728   $191.37   $191.35   $191.40  
  Purchase #3 $138.67   11.523%   $154.6489   $154.65   $154.65   $154.60  
  Purchase #4 $195.63   7.823%   $210.9341   $210.93   $210.95   $210.90  
  Purchase #5 $24.99   5.143%   $26.2752   $26.28   $26.30   $26.30  
  Purchase #6 $87.70   4.477%   $91.6263   $91.63   $91.65   $91.60  
  Purchase #7 $180.49   3.598%   $186.984   $186.98   $187.00   $187.00  
  7 purchase totals = $895.93       $958.4935   $958.49   $958.55   $958.50