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 $53.99   9.561%   $59.152   $59.15   $59.15   $59.20  
  Purchase #2 $96.77   13.668%   $109.9965   $110.00   $110.00   $110.00  
  Purchase #3 $43.88   10.828%   $48.6313   $48.63   $48.65   $48.60  
  Purchase #4 $34.31   13.843%   $39.0595   $39.06   $39.05   $39.10  
  Purchase #5 $190.71   9.502%   $208.8313   $208.83   $208.85   $208.80  
  Purchase #6 $226.68   6.240%   $240.8248   $240.82   $240.80   $240.80  
  Purchase #7 $124.36   8.541%   $134.9816   $134.98   $135.00   $135.00  
  7 purchase totals = $770.70       $841.4770   $841.47   $841.50   $841.50