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 $228.37   3.332%   $235.9793   $235.98   $236.00   $236.00  
  Purchase #2 $185.93   9.145%   $202.9333   $202.93   $202.95   $202.90  
  Purchase #3 $119.62   8.838%   $130.192   $130.19   $130.20   $130.20  
  Purchase #4 $98.97   6.209%   $105.115   $105.12   $105.10   $105.10  
  Purchase #5 $119.82   12.457%   $134.746   $134.75   $134.75   $134.70  
  Purchase #6 $110.93   6.325%   $117.9463   $117.95   $117.95   $117.90  
  Purchase #7 $65.60   8.660%   $71.281   $71.28   $71.30   $71.30  
  7 purchase totals = $929.24       $998.1929   $998.20   $998.25   $998.10