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 $137.57   8.766%   $149.6294   $149.63   $149.65   $149.60  
  Purchase #2 $235.29   13.600%   $267.2894   $267.29   $267.30   $267.30  
  Purchase #3 $158.87   12.792%   $179.1927   $179.19   $179.20   $179.20  
  Purchase #4 $214.77   4.130%   $223.64   $223.64   $223.65   $223.60  
  Purchase #5 $200.56   8.564%   $217.736   $217.74   $217.75   $217.70  
  Purchase #6 $86.73   8.857%   $94.4117   $94.41   $94.40   $94.40  
  Purchase #7 $131.58   6.424%   $140.0327   $140.03   $140.05   $140.00  
  7 purchase totals = $1,165.37       $1,271.9319   $1,271.93   $1,272.00   $1,271.80