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 $184.30   6.138%   $195.6123   $195.61   $195.60   $195.60  
  Purchase #2 $195.45   11.298%   $217.5319   $217.53   $217.55   $217.50  
  Purchase #3 $97.29   12.515%   $109.4658   $109.47   $109.45   $109.50  
  Purchase #4 $119.34   12.777%   $134.5881   $134.59   $134.60   $134.60  
  Purchase #5 $93.61   13.784%   $106.5132   $106.51   $106.50   $106.50  
  Purchase #6 $124.46   12.514%   $140.0349   $140.03   $140.05   $140.00  
  Purchase #7 $93.32   4.806%   $97.805   $97.81   $97.80   $97.80  
  7 purchase totals = $907.77       $1,001.5512   $1,001.55   $1,001.55   $1,001.50