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 $189.40   8.746%   $205.9649   $205.96   $205.95   $206.00  
  Purchase #2 $84.73   13.696%   $96.3346   $96.33   $96.35   $96.30  
  Purchase #3 $70.88   9.192%   $77.3953   $77.40   $77.40   $77.40  
  Purchase #4 $79.34   3.178%   $81.8614   $81.86   $81.85   $81.90  
  Purchase #5 $227.37   8.411%   $246.4941   $246.49   $246.50   $246.50  
  Purchase #6 $192.84   5.185%   $202.8388   $202.84   $202.85   $202.80  
  Purchase #7 $229.35   13.249%   $259.7366   $259.74   $259.75   $259.70  
  7 purchase totals = $1,073.91       $1,170.6257   $1,170.62   $1,170.65   $1,170.60