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 $154.80   7.582%   $166.5369   $166.54   $166.55   $166.50  
  Purchase #2 $208.53   4.545%   $218.0077   $218.01   $218.00   $218.00  
  Purchase #3 $97.26   7.595%   $104.6469   $104.65   $104.65   $104.60  
  Purchase #4 $123.46   3.804%   $128.1564   $128.16   $128.15   $128.20  
  Purchase #5 $226.89   6.158%   $240.8619   $240.86   $240.85   $240.90  
  Purchase #6 $229.36   9.219%   $250.5047   $250.50   $250.50   $250.50  
  Purchase #7 $211.79   12.671%   $238.6259   $238.63   $238.65   $238.60  
  7 purchase totals = $1,252.09       $1,347.3404   $1,347.35   $1,347.35   $1,347.30