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 $86.57   13.276%   $98.063   $98.06   $98.05   $98.10  
  Purchase #2 $178.57   13.469%   $202.6216   $202.62   $202.60   $202.60  
  Purchase #3 $56.57   13.338%   $64.1153   $64.12   $64.10   $64.10  
  Purchase #4 $225.83   8.366%   $244.7229   $244.72   $244.70   $244.70  
  Purchase #5 $73.77   13.152%   $83.4722   $83.47   $83.45   $83.50  
  Purchase #6 $204.91   12.336%   $230.1877   $230.19   $230.20   $230.20  
  Purchase #7 $54.73   12.787%   $61.7283   $61.73   $61.75   $61.70  
  7 purchase totals = $880.95       $984.9110   $984.91   $984.85   $984.90