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 $94.59   9.566%   $103.6385   $103.64   $103.65   $103.60  
  Purchase #2 $198.97   6.664%   $212.2294   $212.23   $212.25   $212.20  
  Purchase #3 $91.75   7.665%   $98.7826   $98.78   $98.80   $98.80  
  Purchase #4 $229.74   6.830%   $245.4312   $245.43   $245.45   $245.40  
  Purchase #5 $44.29   6.660%   $47.2397   $47.24   $47.25   $47.20  
  Purchase #6 $132.59   13.128%   $149.9964   $150.00   $150.00   $150.00  
  Purchase #7 $48.55   11.336%   $54.0536   $54.05   $54.05   $54.10  
  7 purchase totals = $840.48       $911.3714   $911.37   $911.45   $911.30