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 $179.68   12.677%   $202.458   $202.46   $202.45   $202.50  
  Purchase #2 $91.96   8.454%   $99.7343   $99.73   $99.75   $99.70  
  Purchase #3 $36.63   12.170%   $41.0879   $41.09   $41.10   $41.10  
  Purchase #4 $248.47   5.752%   $262.762   $262.76   $262.75   $262.80  
  Purchase #5 $168.52   12.238%   $189.1435   $189.14   $189.15   $189.10  
  Purchase #6 $190.89   7.525%   $205.2545   $205.25   $205.25   $205.30  
  Purchase #7 $79.94   12.255%   $89.7366   $89.74   $89.75   $89.70  
  7 purchase totals = $996.09       $1,090.1768   $1,090.17   $1,090.20   $1,090.20