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 $232.77   6.399%   $247.665   $247.67   $247.65   $247.70  
  Purchase #2 $84.46   6.471%   $89.9254   $89.93   $89.95   $89.90  
  Purchase #3 $16.93   5.535%   $17.8671   $17.87   $17.85   $17.90  
  Purchase #4 $127.71   9.621%   $139.997   $140.00   $140.00   $140.00  
  Purchase #5 $229.65   6.370%   $244.2787   $244.28   $244.30   $244.30  
  Purchase #6 $240.40   9.788%   $263.9304   $263.93   $263.95   $263.90  
  Purchase #7 $213.30   9.647%   $233.8771   $233.88   $233.90   $233.90  
  7 purchase totals = $1,145.22       $1,237.5407   $1,237.56   $1,237.60   $1,237.60