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 $182.47   6.472%   $194.2795   $194.28   $194.30   $194.30  
  Purchase #2 $92.41   13.194%   $104.6026   $104.60   $104.60   $104.60  
  Purchase #3 $106.45   3.361%   $110.0278   $110.03   $110.05   $110.00  
  Purchase #4 $206.94   13.732%   $235.357   $235.36   $235.35   $235.40  
  Purchase #5 $246.39   10.135%   $271.3616   $271.36   $271.35   $271.40  
  Purchase #6 $39.62   8.528%   $42.9988   $43.00   $43.00   $43.00  
  Purchase #7 $19.36   3.629%   $20.0626   $20.06   $20.05   $20.10  
  7 purchase totals = $893.64       $978.6899   $978.69   $978.70   $978.80