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 $53.45   13.682%   $60.763   $60.76   $60.75   $60.80  
  Purchase #2 $62.60   6.632%   $66.7516   $66.75   $66.75   $66.80  
  Purchase #3 $248.87   3.874%   $258.5112   $258.51   $258.50   $258.50  
  Purchase #4 $174.96   8.410%   $189.6741   $189.67   $189.65   $189.70  
  Purchase #5 $17.40   8.741%   $18.9209   $18.92   $18.90   $18.90  
  Purchase #6 $47.97   9.496%   $52.5252   $52.53   $52.55   $52.50  
  Purchase #7 $129.86   11.705%   $145.0601   $145.06   $145.05   $145.10  
  7 purchase totals = $735.11       $792.2061   $792.20   $792.15   $792.30