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 $60.82   13.194%   $68.8446   $68.84   $68.85   $68.80  
  Purchase #2 $123.26   6.371%   $131.1129   $131.11   $131.10   $131.10  
  Purchase #3 $202.26   9.147%   $220.7607   $220.76   $220.75   $220.80  
  Purchase #4 $187.99   13.427%   $213.2314   $213.23   $213.25   $213.20  
  Purchase #5 $61.90   11.348%   $68.9244   $68.92   $68.90   $68.90  
  Purchase #6 $87.77   10.428%   $96.9227   $96.92   $96.90   $96.90  
  Purchase #7 $210.47   11.461%   $234.592   $234.59   $234.60   $234.60  
  7 purchase totals = $934.47       $1,034.3887   $1,034.37   $1,034.35   $1,034.30