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 $207.41   7.603%   $223.1794   $223.18   $223.20   $223.20  
  Purchase #2 $85.75   9.290%   $93.7162   $93.72   $93.70   $93.70  
  Purchase #3 $43.99   8.377%   $47.675   $47.68   $47.70   $47.70  
  Purchase #4 $60.33   5.847%   $63.8575   $63.86   $63.85   $63.90  
  Purchase #5 $184.85   8.598%   $200.7434   $200.74   $200.75   $200.70  
  Purchase #6 $118.85   5.689%   $125.6114   $125.61   $125.60   $125.60  
  Purchase #7 $215.70   5.775%   $228.1567   $228.16   $228.15   $228.20  
  7 purchase totals = $916.88       $982.9396   $982.95   $982.95   $983.00