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 $42.48   8.766%   $46.2038   $46.20   $46.20   $46.20  
  Purchase #2 $180.30   11.287%   $200.6505   $200.65   $200.65   $200.70  
  Purchase #3 $134.49   5.146%   $141.4109   $141.41   $141.40   $141.40  
  Purchase #4 $206.55   7.248%   $221.5207   $221.52   $221.50   $221.50  
  Purchase #5 $169.26   4.456%   $176.8022   $176.80   $176.80   $176.80  
  Purchase #6 $147.83   6.143%   $156.9112   $156.91   $156.90   $156.90  
  Purchase #7 $47.31   6.419%   $50.3468   $50.35   $50.35   $50.30  
  7 purchase totals = $928.22       $993.8461   $993.84   $993.80   $993.80