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 $63.78   8.549%   $69.2326   $69.23   $69.25   $69.20  
  Purchase #2 $141.47   9.766%   $155.286   $155.29   $155.30   $155.30  
  Purchase #3 $112.46   4.170%   $117.1496   $117.15   $117.15   $117.10  
  Purchase #4 $188.53   7.376%   $202.436   $202.44   $202.45   $202.40  
  Purchase #5 $209.74   13.147%   $237.3145   $237.31   $237.30   $237.30  
  Purchase #6 $216.89   13.819%   $246.862   $246.86   $246.85   $246.90  
  Purchase #7 $230.95   6.480%   $245.9156   $245.92   $245.90   $245.90  
  7 purchase totals = $1,163.82       $1,274.1963   $1,274.20   $1,274.20   $1,274.10