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 $242.86   8.357%   $263.1558   $263.16   $263.15   $263.20  
  Purchase #2 $150.57   4.390%   $157.18   $157.18   $157.20   $157.20  
  Purchase #3 $69.50   3.187%   $71.715   $71.72   $71.70   $71.70  
  Purchase #4 $24.82   8.780%   $26.9992   $27.00   $27.00   $27.00  
  Purchase #5 $137.65   12.476%   $154.8232   $154.82   $154.80   $154.80  
  Purchase #6 $179.61   4.294%   $187.3225   $187.32   $187.30   $187.30  
  Purchase #7 $180.64   10.152%   $198.9786   $198.98   $199.00   $199.00  
  7 purchase totals = $985.65       $1,060.1743   $1,060.18   $1,060.15   $1,060.20