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 $88.65   9.124%   $96.7384   $96.74   $96.75   $96.70  
  Purchase #2 $200.81   8.334%   $217.5455   $217.55   $217.55   $217.50  
  Purchase #3 $149.79   11.186%   $166.5455   $166.55   $166.55   $166.50  
  Purchase #4 $14.26   9.132%   $15.5622   $15.56   $15.55   $15.60  
  Purchase #5 $82.98   10.838%   $91.9734   $91.97   $91.95   $92.00  
  Purchase #6 $155.73   12.257%   $174.8178   $174.82   $174.80   $174.80  
  Purchase #7 $7.55   13.133%   $8.5415   $8.54   $8.55   $8.50  
  7 purchase totals = $699.77       $771.7243   $771.73   $771.70   $771.60