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 $248.73   8.330%   $269.4492   $269.45   $269.45   $269.40  
  Purchase #2 $27.53   8.181%   $29.7822   $29.78   $29.80   $29.80  
  Purchase #3 $78.25   10.589%   $86.5359   $86.54   $86.55   $86.50  
  Purchase #4 $181.84   12.720%   $204.97   $204.97   $204.95   $205.00  
  Purchase #5 $87.75   10.370%   $96.8497   $96.85   $96.85   $96.80  
  Purchase #6 $50.36   11.866%   $56.3357   $56.34   $56.35   $56.30  
  Purchase #7 $38.29   13.390%   $43.417   $43.42   $43.40   $43.40  
  7 purchase totals = $712.75       $787.3397   $787.35   $787.35   $787.20