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 $58.69   6.575%   $62.5489   $62.55   $62.55   $62.50  
  Purchase #2 $220.71   13.444%   $250.3823   $250.38   $250.40   $250.40  
  Purchase #3 $11.74   3.297%   $12.1271   $12.13   $12.15   $12.10  
  Purchase #4 $34.85   9.261%   $38.0775   $38.08   $38.10   $38.10  
  Purchase #5 $25.95   3.826%   $26.9428   $26.94   $26.95   $26.90  
  Purchase #6 $241.42   9.668%   $264.7605   $264.76   $264.75   $264.80  
  Purchase #7 $129.91   8.483%   $140.9303   $140.93   $140.95   $140.90  
  7 purchase totals = $723.27       $795.7694   $795.77   $795.85   $795.70