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 $68.38   3.797%   $70.9764   $70.98   $71.00   $71.00  
  Purchase #2 $191.31   7.524%   $205.7042   $205.70   $205.70   $205.70  
  Purchase #3 $192.96   13.133%   $218.3014   $218.30   $218.30   $218.30  
  Purchase #4 $26.40   8.675%   $28.6902   $28.69   $28.70   $28.70  
  Purchase #5 $222.44   10.190%   $245.1066   $245.11   $245.10   $245.10  
  Purchase #6 $241.66   5.257%   $254.3641   $254.36   $254.35   $254.40  
  Purchase #7 $159.42   12.423%   $179.2247   $179.22   $179.20   $179.20  
  7 purchase totals = $1,102.57       $1,202.3676   $1,202.36   $1,202.35   $1,202.40