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 $67.45   9.244%   $73.6851   $73.69   $73.70   $73.70  
  Purchase #2 $148.74   7.112%   $159.3184   $159.32   $159.30   $159.30  
  Purchase #3 $236.35   13.564%   $268.4085   $268.41   $268.40   $268.40  
  Purchase #4 $185.33   3.854%   $192.4726   $192.47   $192.45   $192.50  
  Purchase #5 $197.66   8.740%   $214.9355   $214.94   $214.95   $214.90  
  Purchase #6 $156.51   8.459%   $169.7492   $169.75   $169.75   $169.70  
  Purchase #7 $110.74   8.857%   $120.5482   $120.55   $120.55   $120.50  
  7 purchase totals = $1,102.78       $1,199.1175   $1,199.13   $1,199.10   $1,199.00