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 $137.83   11.461%   $153.6267   $153.63   $153.65   $153.60  
  Purchase #2 $165.85   4.443%   $173.2187   $173.22   $173.20   $173.20  
  Purchase #3 $249.64   8.228%   $270.1804   $270.18   $270.20   $270.20  
  Purchase #4 $94.64   3.116%   $97.589   $97.59   $97.60   $97.60  
  Purchase #5 $98.51   9.474%   $107.8428   $107.84   $107.85   $107.80  
  Purchase #6 $130.37   6.491%   $138.8323   $138.83   $138.85   $138.80  
  Purchase #7 $115.88   8.333%   $125.5363   $125.54   $125.55   $125.50  
  7 purchase totals = $992.72       $1,066.8262   $1,066.83   $1,066.90   $1,066.70