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 $67.89   9.182%   $74.1237   $74.12   $74.10   $74.10  
  Purchase #2 $63.63   11.487%   $70.9392   $70.94   $70.95   $70.90  
  Purchase #3 $49.94   11.734%   $55.8   $55.80   $55.80   $55.80  
  Purchase #4 $23.32   3.160%   $24.0569   $24.06   $24.05   $24.10  
  Purchase #5 $145.29   4.322%   $151.5694   $151.57   $151.55   $151.60  
  Purchase #6 $193.32   3.109%   $199.3303   $199.33   $199.35   $199.30  
  Purchase #7 $205.94   10.169%   $226.882   $226.88   $226.90   $226.90  
  7 purchase totals = $749.33       $802.7015   $802.70   $802.70   $802.70