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 $54.33   13.701%   $61.7738   $61.77   $61.75   $61.80  
  Purchase #2 $184.26   6.585%   $196.3935   $196.39   $196.40   $196.40  
  Purchase #3 $167.35   10.136%   $184.3126   $184.31   $184.30   $184.30  
  Purchase #4 $220.55   10.209%   $243.0659   $243.07   $243.05   $243.10  
  Purchase #5 $201.66   12.256%   $226.3754   $226.38   $226.40   $226.40  
  Purchase #6 $190.28   13.113%   $215.2314   $215.23   $215.25   $215.20  
  Purchase #7 $30.31   12.265%   $34.0275   $34.03   $34.05   $34.00  
  7 purchase totals = $1,048.74       $1,161.1801   $1,161.18   $1,161.20   $1,161.20