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 $171.89   6.589%   $183.2158   $183.22   $183.20   $183.20  
  Purchase #2 $105.50   3.136%   $108.8085   $108.81   $108.80   $108.80  
  Purchase #3 $249.74   12.249%   $280.3307   $280.33   $280.35   $280.30  
  Purchase #4 $17.73   10.796%   $19.6441   $19.64   $19.65   $19.60  
  Purchase #5 $217.80   10.199%   $240.0134   $240.01   $240.00   $240.00  
  Purchase #6 $22.66   9.623%   $24.8406   $24.84   $24.85   $24.80  
  Purchase #7 $244.41   5.125%   $256.936   $256.94   $256.95   $256.90  
  7 purchase totals = $1,029.73       $1,113.7891   $1,113.79   $1,113.80   $1,113.60