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 $88.59   3.309%   $91.5214   $91.52   $91.50   $91.50  
  Purchase #2 $221.41   8.354%   $239.9066   $239.91   $239.90   $239.90  
  Purchase #3 $98.30   13.313%   $111.3867   $111.39   $111.40   $111.40  
  Purchase #4 $56.78   6.460%   $60.448   $60.45   $60.45   $60.40  
  Purchase #5 $207.48   12.121%   $232.6287   $232.63   $232.65   $232.60  
  Purchase #6 $55.71   3.804%   $57.8292   $57.83   $57.85   $57.80  
  Purchase #7 $245.70   8.617%   $266.872   $266.87   $266.85   $266.90  
  7 purchase totals = $973.97       $1,060.5926   $1,060.60   $1,060.60   $1,060.50