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 $189.34   6.287%   $201.2438   $201.24   $201.25   $201.20  
  Purchase #2 $184.54   11.519%   $205.7972   $205.80   $205.80   $205.80  
  Purchase #3 $10.38   12.481%   $11.6755   $11.68   $11.70   $11.70  
  Purchase #4 $102.40   12.292%   $114.987   $114.99   $115.00   $115.00  
  Purchase #5 $55.65   8.235%   $60.2328   $60.23   $60.25   $60.20  
  Purchase #6 $106.68   6.269%   $113.3678   $113.37   $113.35   $113.40  
  Purchase #7 $145.72   11.647%   $162.692   $162.69   $162.70   $162.70  
  7 purchase totals = $794.71       $869.9961   $870.00   $870.05   $870.00