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 $168.42   10.763%   $186.547   $186.55   $186.55   $186.50  
  Purchase #2 $41.96   7.730%   $45.2035   $45.20   $45.20   $45.20  
  Purchase #3 $216.47   5.259%   $227.8542   $227.85   $227.85   $227.90  
  Purchase #4 $59.83   6.140%   $63.5036   $63.50   $63.50   $63.50  
  Purchase #5 $237.98   8.419%   $258.0155   $258.02   $258.00   $258.00  
  Purchase #6 $84.75   12.368%   $95.2319   $95.23   $95.25   $95.20  
  Purchase #7 $66.79   10.551%   $73.837   $73.84   $73.85   $73.80  
  7 purchase totals = $876.20       $950.1927   $950.19   $950.20   $950.10