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 $217.47   10.138%   $239.5171   $239.52   $239.50   $239.50  
  Purchase #2 $200.91   5.483%   $211.9259   $211.93   $211.95   $211.90  
  Purchase #3 $26.90   12.328%   $30.2162   $30.22   $30.20   $30.20  
  Purchase #4 $183.31   9.859%   $201.3825   $201.38   $201.40   $201.40  
  Purchase #5 $92.41   4.736%   $96.7865   $96.79   $96.80   $96.80  
  Purchase #6 $150.90   8.614%   $163.8985   $163.90   $163.90   $163.90  
  Purchase #7 $149.37   7.273%   $160.2337   $160.23   $160.25   $160.20  
  7 purchase totals = $1,021.27       $1,103.9604   $1,103.97   $1,104.00   $1,103.90