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 $55.95   9.553%   $61.2949   $61.29   $61.30   $61.30  
  Purchase #2 $188.30   12.391%   $211.6323   $211.63   $211.65   $211.60  
  Purchase #3 $55.41   13.771%   $63.0405   $63.04   $63.05   $63.00  
  Purchase #4 $236.62   13.541%   $268.6607   $268.66   $268.65   $268.70  
  Purchase #5 $193.70   6.754%   $206.7825   $206.78   $206.80   $206.80  
  Purchase #6 $58.72   3.272%   $60.6413   $60.64   $60.65   $60.60  
  Purchase #7 $41.82   9.395%   $45.749   $45.75   $45.75   $45.70  
  7 purchase totals = $830.52       $917.8012   $917.79   $917.85   $917.70