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 $152.94   8.556%   $166.0255   $166.03   $166.05   $166.00  
  Purchase #2 $179.48   12.865%   $202.5701   $202.57   $202.55   $202.60  
  Purchase #3 $163.82   6.697%   $174.791   $174.79   $174.80   $174.80  
  Purchase #4 $248.27   9.414%   $271.6421   $271.64   $271.65   $271.60  
  Purchase #5 $91.74   6.531%   $97.7315   $97.73   $97.75   $97.70  
  Purchase #6 $234.81   9.828%   $257.8871   $257.89   $257.90   $257.90  
  Purchase #7 $233.42   12.529%   $262.6652   $262.67   $262.65   $262.70  
  7 purchase totals = $1,304.48       $1,433.3125   $1,433.32   $1,433.35   $1,433.30