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 $108.52   13.869%   $123.5706   $123.57   $123.55   $123.60  
  Purchase #2 $84.90   10.684%   $93.9707   $93.97   $93.95   $94.00  
  Purchase #3 $213.33   10.176%   $235.0385   $235.04   $235.05   $235.00  
  Purchase #4 $193.26   11.164%   $214.8355   $214.84   $214.85   $214.80  
  Purchase #5 $49.43   6.712%   $52.7477   $52.75   $52.75   $52.70  
  Purchase #6 $125.37   11.635%   $139.9568   $139.96   $139.95   $140.00  
  Purchase #7 $78.75   8.107%   $85.1343   $85.13   $85.15   $85.10  
  7 purchase totals = $853.56       $945.2541   $945.26   $945.25   $945.20