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 $34.67   4.742%   $36.3141   $36.31   $36.30   $36.30  
  Purchase #2 $180.37   7.523%   $193.9392   $193.94   $193.95   $193.90  
  Purchase #3 $141.86   11.343%   $157.9512   $157.95   $157.95   $158.00  
  Purchase #4 $202.80   10.487%   $224.0676   $224.07   $224.05   $224.10  
  Purchase #5 $46.51   9.421%   $50.8917   $50.89   $50.90   $50.90  
  Purchase #6 $165.65   6.806%   $176.9241   $176.92   $176.90   $176.90  
  Purchase #7 $187.78   5.871%   $198.8046   $198.80   $198.80   $198.80  
  7 purchase totals = $959.64       $1,038.8925   $1,038.88   $1,038.85   $1,038.90