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 $57.41   11.570%   $64.0523   $64.05   $64.05   $64.10  
  Purchase #2 $151.72   4.603%   $158.7037   $158.70   $158.70   $158.70  
  Purchase #3 $122.40   5.707%   $129.3854   $129.39   $129.40   $129.40  
  Purchase #4 $103.26   5.368%   $108.803   $108.80   $108.80   $108.80  
  Purchase #5 $150.58   7.602%   $162.0271   $162.03   $162.05   $162.00  
  Purchase #6 $157.54   11.210%   $175.2002   $175.20   $175.20   $175.20  
  Purchase #7 $185.80   9.196%   $202.8862   $202.89   $202.90   $202.90  
  7 purchase totals = $928.71       $1,001.0579   $1,001.06   $1,001.10   $1,001.10