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 $41.65   5.146%   $43.7933   $43.79   $43.80   $43.80  
  Purchase #2 $229.98   3.226%   $237.3992   $237.40   $237.40   $237.40  
  Purchase #3 $104.34   8.401%   $113.1056   $113.11   $113.10   $113.10  
  Purchase #4 $174.48   13.178%   $197.473   $197.47   $197.45   $197.50  
  Purchase #5 $214.40   5.511%   $226.2156   $226.22   $226.20   $226.20  
  Purchase #6 $67.84   3.190%   $70.0041   $70.00   $70.00   $70.00  
  Purchase #7 $155.54   10.547%   $171.9448   $171.94   $171.95   $171.90  
  7 purchase totals = $988.23       $1,059.9356   $1,059.93   $1,059.90   $1,059.90