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 $70.92   8.432%   $76.9   $76.90   $76.90   $76.90  
  Purchase #2 $240.35   13.593%   $273.0208   $273.02   $273.00   $273.00  
  Purchase #3 $8.43   11.667%   $9.4135   $9.41   $9.40   $9.40  
  Purchase #4 $9.67   13.569%   $10.9821   $10.98   $11.00   $11.00  
  Purchase #5 $188.61   13.617%   $214.293   $214.29   $214.30   $214.30  
  Purchase #6 $221.93   10.453%   $245.1283   $245.13   $245.15   $245.10  
  Purchase #7 $240.36   8.563%   $260.942   $260.94   $260.95   $260.90  
  7 purchase totals = $980.27       $1,090.6797   $1,090.67   $1,090.70   $1,090.60