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 $10.73   9.540%   $11.7536   $11.75   $11.75   $11.80  
  Purchase #2 $93.89   13.277%   $106.3558   $106.36   $106.35   $106.40  
  Purchase #3 $182.38   12.690%   $205.524   $205.52   $205.50   $205.50  
  Purchase #4 $167.71   10.481%   $185.2877   $185.29   $185.30   $185.30  
  Purchase #5 $163.30   3.546%   $169.0906   $169.09   $169.10   $169.10  
  Purchase #6 $166.64   11.686%   $186.1136   $186.11   $186.10   $186.10  
  Purchase #7 $199.51   3.424%   $206.3412   $206.34   $206.35   $206.30  
  7 purchase totals = $984.16       $1,070.4665   $1,070.46   $1,070.45   $1,070.50