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 $89.55   7.123%   $95.9286   $95.93   $95.95   $95.90  
  Purchase #2 $126.43   7.227%   $135.5671   $135.57   $135.55   $135.60  
  Purchase #3 $65.52   5.176%   $68.9113   $68.91   $68.90   $68.90  
  Purchase #4 $113.63   12.233%   $127.5304   $127.53   $127.55   $127.50  
  Purchase #5 $211.77   10.819%   $234.6814   $234.68   $234.70   $234.70  
  Purchase #6 $44.95   4.810%   $47.1121   $47.11   $47.10   $47.10  
  Purchase #7 $183.65   9.417%   $200.9443   $200.94   $200.95   $200.90  
  7 purchase totals = $835.50       $910.6752   $910.67   $910.70   $910.60