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 $195.53   9.792%   $214.6763   $214.68   $214.70   $214.70  
  Purchase #2 $67.97   5.421%   $71.6547   $71.65   $71.65   $71.70  
  Purchase #3 $7.57   11.828%   $8.4654   $8.47   $8.45   $8.50  
  Purchase #4 $131.34   12.136%   $147.2794   $147.28   $147.30   $147.30  
  Purchase #5 $178.53   8.813%   $194.2638   $194.26   $194.25   $194.30  
  Purchase #6 $191.93   9.163%   $209.5165   $209.52   $209.50   $209.50  
  Purchase #7 $13.70   3.399%   $14.1657   $14.17   $14.15   $14.20  
  7 purchase totals = $786.57       $860.0218   $860.03   $860.00   $860.20