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 $54.29   13.147%   $61.4275   $61.43   $61.45   $61.40  
  Purchase #2 $153.74   8.609%   $166.9755   $166.98   $167.00   $167.00  
  Purchase #3 $192.42   5.514%   $203.03   $203.03   $203.05   $203.00  
  Purchase #4 $211.25   7.299%   $226.6691   $226.67   $226.65   $226.70  
  Purchase #5 $109.39   12.858%   $123.4554   $123.46   $123.45   $123.50  
  Purchase #6 $221.30   6.748%   $236.2333   $236.23   $236.25   $236.20  
  Purchase #7 $247.70   6.679%   $264.2439   $264.24   $264.25   $264.20  
  7 purchase totals = $1,190.09       $1,282.0347   $1,282.04   $1,282.10   $1,282.00