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 $222.65   3.601%   $230.6676   $230.67   $230.65   $230.70  
  Purchase #2 $167.30   10.272%   $184.4851   $184.49   $184.50   $184.50  
  Purchase #3 $219.86   7.654%   $236.6881   $236.69   $236.70   $236.70  
  Purchase #4 $77.97   9.840%   $85.6422   $85.64   $85.65   $85.60  
  Purchase #5 $98.86   5.704%   $104.499   $104.50   $104.50   $104.50  
  Purchase #6 $244.65   10.804%   $271.082   $271.08   $271.10   $271.10  
  Purchase #7 $65.97   11.859%   $73.7934   $73.79   $73.80   $73.80  
  7 purchase totals = $1,097.26       $1,186.8574   $1,186.86   $1,186.90   $1,186.90