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 $131.57   11.487%   $146.6834   $146.68   $146.70   $146.70  
  Purchase #2 $128.84   13.793%   $146.6109   $146.61   $146.60   $146.60  
  Purchase #3 $234.65   11.516%   $261.6723   $261.67   $261.65   $261.70  
  Purchase #4 $160.35   3.246%   $165.555   $165.56   $165.55   $165.60  
  Purchase #5 $200.63   11.156%   $223.0123   $223.01   $223.00   $223.00  
  Purchase #6 $60.53   3.302%   $62.5287   $62.53   $62.55   $62.50  
  Purchase #7 $239.89   7.274%   $257.3396   $257.34   $257.35   $257.30  
  7 purchase totals = $1,156.46       $1,263.4022   $1,263.40   $1,263.40   $1,263.40