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 $188.55   11.814%   $210.8253   $210.83   $210.85   $210.80  
  Purchase #2 $177.87   3.573%   $184.2253   $184.23   $184.25   $184.20  
  Purchase #3 $167.66   8.751%   $182.3319   $182.33   $182.35   $182.30  
  Purchase #4 $13.42   8.379%   $14.5445   $14.54   $14.55   $14.50  
  Purchase #5 $116.94   12.477%   $131.5306   $131.53   $131.55   $131.50  
  Purchase #6 $99.54   7.259%   $106.7656   $106.77   $106.75   $106.80  
  Purchase #7 $123.98   9.640%   $135.9317   $135.93   $135.95   $135.90  
  7 purchase totals = $887.96       $966.1549   $966.16   $966.25   $966.00