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 $214.30   10.242%   $236.2486   $236.25   $236.25   $236.20  
  Purchase #2 $189.42   8.296%   $205.1343   $205.13   $205.15   $205.10  
  Purchase #3 $245.76   6.734%   $262.3095   $262.31   $262.30   $262.30  
  Purchase #4 $203.55   5.388%   $214.5173   $214.52   $214.50   $214.50  
  Purchase #5 $29.99   12.189%   $33.6455   $33.65   $33.65   $33.60  
  Purchase #6 $163.75   3.418%   $169.347   $169.35   $169.35   $169.30  
  Purchase #7 $118.71   10.636%   $131.336   $131.34   $131.35   $131.30  
  7 purchase totals = $1,165.48       $1,252.5382   $1,252.55   $1,252.55   $1,252.30