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 $97.91   6.253%   $104.0323   $104.03   $104.05   $104.00  
  Purchase #2 $177.43   8.142%   $191.8764   $191.88   $191.90   $191.90  
  Purchase #3 $51.45   6.560%   $54.8251   $54.83   $54.85   $54.80  
  Purchase #4 $174.53   12.121%   $195.6848   $195.68   $195.70   $195.70  
  Purchase #5 $43.57   6.724%   $46.4996   $46.50   $46.50   $46.50  
  Purchase #6 $178.31   13.723%   $202.7795   $202.78   $202.80   $202.80  
  Purchase #7 $245.62   5.802%   $259.8709   $259.87   $259.85   $259.90  
  7 purchase totals = $968.82       $1,055.5686   $1,055.57   $1,055.65   $1,055.60