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 $160.34   8.263%   $173.5889   $173.59   $173.60   $173.60  
  Purchase #2 $250.41   3.646%   $259.5399   $259.54   $259.55   $259.50  
  Purchase #3 $189.30   4.128%   $197.1143   $197.11   $197.10   $197.10  
  Purchase #4 $206.46   8.763%   $224.5521   $224.55   $224.55   $224.60  
  Purchase #5 $186.59   13.379%   $211.5539   $211.55   $211.55   $211.60  
  Purchase #6 $183.27   11.663%   $204.6448   $204.64   $204.65   $204.60  
  Purchase #7 $90.80   4.690%   $95.0585   $95.06   $95.05   $95.10  
  7 purchase totals = $1,267.17       $1,366.0524   $1,366.04   $1,366.05   $1,366.10