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 $117.64   11.294%   $130.9263   $130.93   $130.95   $130.90  
  Purchase #2 $196.68   13.307%   $222.8522   $222.85   $222.85   $222.90  
  Purchase #3 $42.75   11.657%   $47.7334   $47.73   $47.75   $47.70  
  Purchase #4 $26.81   6.395%   $28.5245   $28.52   $28.50   $28.50  
  Purchase #5 $216.95   8.763%   $235.9613   $235.96   $235.95   $236.00  
  Purchase #6 $89.93   6.640%   $95.9014   $95.90   $95.90   $95.90  
  Purchase #7 $195.84   9.582%   $214.6054   $214.61   $214.60   $214.60  
  7 purchase totals = $886.60       $976.5045   $976.50   $976.50   $976.50