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 $162.67   7.496%   $174.8637   $174.86   $174.85   $174.90  
  Purchase #2 $200.96   6.471%   $213.9641   $213.96   $213.95   $214.00  
  Purchase #3 $61.29   6.609%   $65.3407   $65.34   $65.35   $65.30  
  Purchase #4 $5.96   11.775%   $6.6618   $6.66   $6.65   $6.70  
  Purchase #5 $245.25   3.452%   $253.716   $253.72   $253.70   $253.70  
  Purchase #6 $66.40   5.121%   $69.8003   $69.80   $69.80   $69.80  
  Purchase #7 $224.87   13.542%   $255.3219   $255.32   $255.30   $255.30  
  7 purchase totals = $967.40       $1,039.6685   $1,039.66   $1,039.60   $1,039.70