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 $88.41   11.392%   $98.4817   $98.48   $98.50   $98.50  
  Purchase #2 $85.60   9.711%   $93.9126   $93.91   $93.90   $93.90  
  Purchase #3 $250.94   11.190%   $279.0202   $279.02   $279.00   $279.00  
  Purchase #4 $76.25   4.616%   $79.7697   $79.77   $79.75   $79.80  
  Purchase #5 $104.65   3.662%   $108.4823   $108.48   $108.50   $108.50  
  Purchase #6 $125.84   4.129%   $131.0359   $131.04   $131.05   $131.00  
  Purchase #7 $223.71   5.132%   $235.1908   $235.19   $235.20   $235.20  
  7 purchase totals = $955.40       $1,025.8932   $1,025.89   $1,025.90   $1,025.90