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 $234.92   11.572%   $262.1049   $262.10   $262.10   $262.10  
  Purchase #2 $109.30   6.866%   $116.8045   $116.80   $116.80   $116.80  
  Purchase #3 $35.29   4.290%   $36.8039   $36.80   $36.80   $36.80  
  Purchase #4 $229.86   7.259%   $246.5455   $246.55   $246.55   $246.50  
  Purchase #5 $214.86   3.841%   $223.1128   $223.11   $223.10   $223.10  
  Purchase #6 $186.87   5.293%   $196.761   $196.76   $196.75   $196.80  
  Purchase #7 $149.28   8.496%   $161.9628   $161.96   $161.95   $162.00  
  7 purchase totals = $1,160.38       $1,244.0954   $1,244.08   $1,244.05   $1,244.10