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 $69.91   8.482%   $75.8398   $75.84   $75.85   $75.80  
  Purchase #2 $59.59   6.770%   $63.6242   $63.62   $63.60   $63.60  
  Purchase #3 $204.71   10.251%   $225.6948   $225.69   $225.70   $225.70  
  Purchase #4 $90.99   13.285%   $103.078   $103.08   $103.10   $103.10  
  Purchase #5 $91.32   8.342%   $98.9379   $98.94   $98.95   $98.90  
  Purchase #6 $182.90   6.249%   $194.3294   $194.33   $194.35   $194.30  
  Purchase #7 $59.57   8.279%   $64.5018   $64.50   $64.50   $64.50  
  7 purchase totals = $758.99       $826.0059   $826.00   $826.05   $825.90