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 $59.37   8.681%   $64.5239   $64.52   $64.50   $64.50  
  Purchase #2 $203.79   13.634%   $231.5747   $231.57   $231.55   $231.60  
  Purchase #3 $130.93   3.776%   $135.8739   $135.87   $135.85   $135.90  
  Purchase #4 $188.81   8.802%   $205.4291   $205.43   $205.45   $205.40  
  Purchase #5 $208.36   10.307%   $229.8357   $229.84   $229.85   $229.80  
  Purchase #6 $49.59   4.312%   $51.7283   $51.73   $51.75   $51.70  
  Purchase #7 $113.96   10.102%   $125.4722   $125.47   $125.45   $125.50  
  7 purchase totals = $954.81       $1,044.4378   $1,044.43   $1,044.40   $1,044.40