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 $89.95   9.655%   $98.6347   $98.63   $98.65   $98.60  
  Purchase #2 $231.68   13.660%   $263.3275   $263.33   $263.35   $263.30  
  Purchase #3 $21.89   5.862%   $23.1732   $23.17   $23.15   $23.20  
  Purchase #4 $171.33   11.709%   $191.391   $191.39   $191.40   $191.40  
  Purchase #5 $8.25   8.557%   $8.956   $8.96   $8.95   $9.00  
  Purchase #6 $206.51   10.283%   $227.7454   $227.75   $227.75   $227.70  
  Purchase #7 $106.34   13.118%   $120.2897   $120.29   $120.30   $120.30  
  7 purchase totals = $835.95       $933.5175   $933.52   $933.55   $933.50