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 $218.50   6.633%   $232.9931   $232.99   $233.00   $233.00  
  Purchase #2 $161.54   10.738%   $178.8862   $178.89   $178.90   $178.90  
  Purchase #3 $23.84   9.638%   $26.1377   $26.14   $26.15   $26.10  
  Purchase #4 $137.49   10.516%   $151.9484   $151.95   $151.95   $151.90  
  Purchase #5 $180.85   5.800%   $191.3393   $191.34   $191.35   $191.30  
  Purchase #6 $156.74   3.282%   $161.8842   $161.88   $161.90   $161.90  
  Purchase #7 $113.72   12.857%   $128.341   $128.34   $128.35   $128.30  
  7 purchase totals = $992.68       $1,071.5299   $1,071.53   $1,071.60   $1,071.40