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 $226.31   13.844%   $257.6404   $257.64   $257.65   $257.60  
  Purchase #2 $117.89   9.298%   $128.8514   $128.85   $128.85   $128.90  
  Purchase #3 $173.47   8.621%   $188.4248   $188.42   $188.40   $188.40  
  Purchase #4 $33.35   7.562%   $35.8719   $35.87   $35.85   $35.90  
  Purchase #5 $150.46   4.587%   $157.3616   $157.36   $157.35   $157.40  
  Purchase #6 $157.56   13.272%   $178.4714   $178.47   $178.45   $178.50  
  Purchase #7 $54.91   6.146%   $58.2848   $58.28   $58.30   $58.30  
  7 purchase totals = $913.95       $1,004.9063   $1,004.89   $1,004.85   $1,005.00