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 $59.83   11.350%   $66.6207   $66.62   $66.60   $66.60  
  Purchase #2 $145.37   6.169%   $154.3379   $154.34   $154.35   $154.30  
  Purchase #3 $164.52   3.616%   $170.469   $170.47   $170.45   $170.50  
  Purchase #4 $200.45   6.113%   $212.7035   $212.70   $212.70   $212.70  
  Purchase #5 $35.93   13.292%   $40.7058   $40.71   $40.70   $40.70  
  Purchase #6 $149.60   6.390%   $159.1594   $159.16   $159.15   $159.20  
  Purchase #7 $212.53   3.850%   $220.7124   $220.71   $220.70   $220.70  
  7 purchase totals = $968.23       $1,024.7087   $1,024.71   $1,024.65   $1,024.70