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 $60.86   12.681%   $68.5777   $68.58   $68.60   $68.60  
  Purchase #2 $232.99   3.803%   $241.8506   $241.85   $241.85   $241.90  
  Purchase #3 $135.68   5.648%   $143.3432   $143.34   $143.35   $143.30  
  Purchase #4 $81.71   11.774%   $91.3305   $91.33   $91.35   $91.30  
  Purchase #5 $14.41   11.569%   $16.0771   $16.08   $16.10   $16.10  
  Purchase #6 $56.26   7.654%   $60.5661   $60.57   $60.55   $60.60  
  Purchase #7 $135.81   8.699%   $147.6241   $147.62   $147.60   $147.60  
  7 purchase totals = $717.72       $769.3693   $769.37   $769.40   $769.40