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 $63.61   5.763%   $67.2758   $67.28   $67.30   $67.30  
  Purchase #2 $169.47   7.188%   $181.6515   $181.65   $181.65   $181.70  
  Purchase #3 $207.65   11.795%   $232.1423   $232.14   $232.15   $232.10  
  Purchase #4 $157.52   4.609%   $164.7801   $164.78   $164.80   $164.80  
  Purchase #5 $46.26   7.453%   $49.7078   $49.71   $49.70   $49.70  
  Purchase #6 $116.84   9.874%   $128.3768   $128.38   $128.40   $128.40  
  Purchase #7 $20.34   13.608%   $23.1079   $23.11   $23.10   $23.10  
  7 purchase totals = $781.69       $847.0422   $847.05   $847.10   $847.10