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 $214.87   10.111%   $236.5955   $236.60   $236.60   $236.60  
  Purchase #2 $176.92   6.455%   $188.3402   $188.34   $188.35   $188.30  
  Purchase #3 $108.50   11.653%   $121.1435   $121.14   $121.15   $121.10  
  Purchase #4 $23.68   9.216%   $25.8623   $25.86   $25.85   $25.90  
  Purchase #5 $50.42   13.625%   $57.2897   $57.29   $57.30   $57.30  
  Purchase #6 $84.36   4.703%   $88.3275   $88.33   $88.35   $88.30  
  Purchase #7 $120.43   11.865%   $134.719   $134.72   $134.70   $134.70  
  7 purchase totals = $779.18       $852.2777   $852.28   $852.30   $852.20