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 $155.77   13.418%   $176.6712   $176.67   $176.65   $176.70  
  Purchase #2 $125.41   12.370%   $140.9232   $140.92   $140.90   $140.90  
  Purchase #3 $236.49   12.268%   $265.5026   $265.50   $265.50   $265.50  
  Purchase #4 $88.50   11.331%   $98.5279   $98.53   $98.55   $98.50  
  Purchase #5 $8.33   7.658%   $8.9679   $8.97   $8.95   $9.00  
  Purchase #6 $166.80   5.803%   $176.4794   $176.48   $176.50   $176.50  
  Purchase #7 $153.36   7.797%   $165.3175   $165.32   $165.30   $165.30  
  7 purchase totals = $934.66       $1,032.3897   $1,032.39   $1,032.35   $1,032.40