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 $87.75   12.117%   $98.3827   $98.38   $98.40   $98.40  
  Purchase #2 $89.86   4.841%   $94.2101   $94.21   $94.20   $94.20  
  Purchase #3 $65.73   6.130%   $69.7592   $69.76   $69.75   $69.80  
  Purchase #4 $216.75   3.353%   $224.0176   $224.02   $224.00   $224.00  
  Purchase #5 $213.98   4.343%   $223.2732   $223.27   $223.25   $223.30  
  Purchase #6 $237.91   12.773%   $268.2982   $268.30   $268.30   $268.30  
  Purchase #7 $110.71   9.237%   $120.9363   $120.94   $120.95   $120.90  
  7 purchase totals = $1,022.69       $1,098.8773   $1,098.88   $1,098.85   $1,098.90