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 $147.86   4.209%   $154.0834   $154.08   $154.10   $154.10  
  Purchase #2 $182.49   3.177%   $188.2877   $188.29   $188.30   $188.30  
  Purchase #3 $91.73   3.529%   $94.9672   $94.97   $94.95   $95.00  
  Purchase #4 $135.91   9.278%   $148.5197   $148.52   $148.50   $148.50  
  Purchase #5 $63.93   3.754%   $66.3299   $66.33   $66.35   $66.30  
  Purchase #6 $59.99   8.658%   $65.1839   $65.18   $65.20   $65.20  
  Purchase #7 $120.68   5.792%   $127.6698   $127.67   $127.65   $127.70  
  7 purchase totals = $802.59       $845.0416   $845.04   $845.05   $845.10