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 $63.54   10.493%   $70.2073   $70.21   $70.20   $70.20  
  Purchase #2 $169.89   5.131%   $178.6071   $178.61   $178.60   $178.60  
  Purchase #3 $161.78   8.511%   $175.5491   $175.55   $175.55   $175.50  
  Purchase #4 $239.93   11.415%   $267.318   $267.32   $267.30   $267.30  
  Purchase #5 $156.48   3.208%   $161.4999   $161.50   $161.50   $161.50  
  Purchase #6 $26.52   5.811%   $28.0611   $28.06   $28.05   $28.10  
  Purchase #7 $135.86   9.602%   $148.9053   $148.91   $148.90   $148.90  
  7 purchase totals = $954.00       $1,030.1478   $1,030.16   $1,030.10   $1,030.10