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 $39.90   8.653%   $43.3525   $43.35   $43.35   $43.40  
  Purchase #2 $200.54   3.742%   $208.0442   $208.04   $208.05   $208.00  
  Purchase #3 $215.50   9.159%   $235.2376   $235.24   $235.25   $235.20  
  Purchase #4 $14.38   8.276%   $15.5701   $15.57   $15.55   $15.60  
  Purchase #5 $124.79   9.793%   $137.0107   $137.01   $137.00   $137.00  
  Purchase #6 $81.70   4.413%   $85.3054   $85.31   $85.30   $85.30  
  Purchase #7 $200.37   12.551%   $225.5184   $225.52   $225.50   $225.50  
  7 purchase totals = $877.18       $950.0389   $950.04   $950.00   $950.00