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 $98.70   5.590%   $104.2173   $104.22   $104.20   $104.20  
  Purchase #2 $219.69   3.251%   $226.8321   $226.83   $226.85   $226.80  
  Purchase #3 $26.38   8.680%   $28.6698   $28.67   $28.65   $28.70  
  Purchase #4 $158.52   8.515%   $172.018   $172.02   $172.00   $172.00  
  Purchase #5 $63.77   6.796%   $68.1038   $68.10   $68.10   $68.10  
  Purchase #6 $130.91   13.546%   $148.6431   $148.64   $148.65   $148.60  
  Purchase #7 $162.74   13.458%   $184.6415   $184.64   $184.65   $184.60  
  7 purchase totals = $860.71       $933.1256   $933.12   $933.10   $933.00