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 $225.73   8.825%   $245.6507   $245.65   $245.65   $245.70  
  Purchase #2 $205.51   3.596%   $212.9001   $212.90   $212.90   $212.90  
  Purchase #3 $45.74   5.677%   $48.3367   $48.34   $48.35   $48.30  
  Purchase #4 $113.26   6.202%   $120.2844   $120.28   $120.30   $120.30  
  Purchase #5 $51.48   9.170%   $56.2007   $56.20   $56.20   $56.20  
  Purchase #6 $104.99   7.311%   $112.6658   $112.67   $112.65   $112.70  
  Purchase #7 $216.38   5.849%   $229.0361   $229.04   $229.05   $229.00  
  7 purchase totals = $963.09       $1,025.0745   $1,025.08   $1,025.10   $1,025.10