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 $136.53   12.230%   $153.2276   $153.23   $153.25   $153.20  
  Purchase #2 $128.69   7.763%   $138.6802   $138.68   $138.70   $138.70  
  Purchase #3 $193.85   3.284%   $200.216   $200.22   $200.20   $200.20  
  Purchase #4 $35.98   9.350%   $39.3441   $39.34   $39.35   $39.30  
  Purchase #5 $161.79   5.599%   $170.8486   $170.85   $170.85   $170.80  
  Purchase #6 $126.70   3.191%   $130.743   $130.74   $130.75   $130.70  
  Purchase #7 $34.75   3.874%   $36.0962   $36.10   $36.10   $36.10  
  7 purchase totals = $818.29       $869.1557   $869.16   $869.20   $869.00