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 $249.74   5.581%   $263.678   $263.68   $263.70   $263.70  
  Purchase #2 $148.56   12.123%   $166.5699   $166.57   $166.55   $166.60  
  Purchase #3 $81.30   8.130%   $87.9097   $87.91   $87.90   $87.90  
  Purchase #4 $10.52   7.237%   $11.2813   $11.28   $11.30   $11.30  
  Purchase #5 $43.37   12.845%   $48.9409   $48.94   $48.95   $48.90  
  Purchase #6 $229.57   5.713%   $242.6853   $242.69   $242.70   $242.70  
  Purchase #7 $199.61   7.250%   $214.0817   $214.08   $214.10   $214.10  
  7 purchase totals = $962.67       $1,035.1468   $1,035.15   $1,035.20   $1,035.20