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 $149.83   5.621%   $158.2519   $158.25   $158.25   $158.30  
  Purchase #2 $212.42   11.428%   $236.6954   $236.70   $236.70   $236.70  
  Purchase #3 $65.96   9.389%   $72.153   $72.15   $72.15   $72.20  
  Purchase #4 $80.73   4.782%   $84.5905   $84.59   $84.60   $84.60  
  Purchase #5 $172.58   3.239%   $178.1699   $178.17   $178.15   $178.20  
  Purchase #6 $25.52   9.723%   $28.0013   $28.00   $28.00   $28.00  
  Purchase #7 $148.28   13.540%   $168.3571   $168.36   $168.35   $168.40  
  7 purchase totals = $855.32       $926.2191   $926.22   $926.20   $926.40