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 $206.91   11.172%   $230.026   $230.03   $230.05   $230.00  
  Purchase #2 $29.63   12.330%   $33.2834   $33.28   $33.30   $33.30  
  Purchase #3 $74.70   5.239%   $78.6135   $78.61   $78.60   $78.60  
  Purchase #4 $64.47   8.195%   $69.7533   $69.75   $69.75   $69.80  
  Purchase #5 $75.71   6.471%   $80.6092   $80.61   $80.60   $80.60  
  Purchase #6 $229.72   7.771%   $247.5715   $247.57   $247.55   $247.60  
  Purchase #7 $26.81   9.520%   $29.3623   $29.36   $29.35   $29.40  
  7 purchase totals = $707.95       $769.2192   $769.21   $769.20   $769.30