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 $217.65   6.867%   $232.596   $232.60   $232.60   $232.60  
  Purchase #2 $83.28   4.289%   $86.8519   $86.85   $86.85   $86.90  
  Purchase #3 $107.93   12.739%   $121.6792   $121.68   $121.70   $121.70  
  Purchase #4 $46.63   6.668%   $49.7393   $49.74   $49.75   $49.70  
  Purchase #5 $146.34   6.607%   $156.0087   $156.01   $156.00   $156.00  
  Purchase #6 $24.91   3.214%   $25.7106   $25.71   $25.70   $25.70  
  Purchase #7 $18.70   3.797%   $19.41   $19.41   $19.40   $19.40  
  7 purchase totals = $645.44       $691.9957   $692.00   $692.00   $692.00