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 $101.64   7.844%   $109.6126   $109.61   $109.60   $109.60  
  Purchase #2 $161.67   11.198%   $179.7738   $179.77   $179.75   $179.80  
  Purchase #3 $28.96   5.661%   $30.5994   $30.60   $30.60   $30.60  
  Purchase #4 $87.61   9.103%   $95.5851   $95.59   $95.60   $95.60  
  Purchase #5 $227.58   4.146%   $237.0155   $237.02   $237.00   $237.00  
  Purchase #6 $83.34   9.506%   $91.2623   $91.26   $91.25   $91.30  
  Purchase #7 $48.39   7.412%   $51.9767   $51.98   $52.00   $52.00  
  7 purchase totals = $739.19       $795.8254   $795.83   $795.80   $795.90