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 $177.52   3.816%   $184.2942   $184.29   $184.30   $184.30  
  Purchase #2 $184.47   10.407%   $203.6678   $203.67   $203.65   $203.70  
  Purchase #3 $169.82   8.508%   $184.2683   $184.27   $184.25   $184.30  
  Purchase #4 $76.28   3.407%   $78.8789   $78.88   $78.90   $78.90  
  Purchase #5 $154.62   9.868%   $169.8779   $169.88   $169.90   $169.90  
  Purchase #6 $214.47   13.245%   $242.8766   $242.88   $242.90   $242.90  
  Purchase #7 $56.87   6.429%   $60.5262   $60.53   $60.55   $60.50  
  7 purchase totals = $1,034.05       $1,124.3899   $1,124.40   $1,124.45   $1,124.50