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 $228.60   3.477%   $236.5484   $236.55   $236.55   $236.50  
  Purchase #2 $233.90   10.103%   $257.5309   $257.53   $257.55   $257.50  
  Purchase #3 $64.67   9.780%   $70.9947   $70.99   $71.00   $71.00  
  Purchase #4 $112.74   5.352%   $118.7738   $118.77   $118.75   $118.80  
  Purchase #5 $93.32   12.326%   $104.8226   $104.82   $104.80   $104.80  
  Purchase #6 $215.86   11.349%   $240.358   $240.36   $240.35   $240.40  
  Purchase #7 $19.95   10.532%   $22.0511   $22.05   $22.05   $22.10  
  7 purchase totals = $969.04       $1,051.0795   $1,051.07   $1,051.05   $1,051.10