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 $64.67   10.120%   $71.2146   $71.21   $71.20   $71.20  
  Purchase #2 $55.67   8.748%   $60.54   $60.54   $60.55   $60.50  
  Purchase #3 $8.83   12.447%   $9.9291   $9.93   $9.95   $9.90  
  Purchase #4 $147.60   5.421%   $155.6014   $155.60   $155.60   $155.60  
  Purchase #5 $238.54   5.483%   $251.6191   $251.62   $251.60   $251.60  
  Purchase #6 $113.43   8.433%   $122.9956   $123.00   $123.00   $123.00  
  Purchase #7 $33.32   4.238%   $34.7321   $34.73   $34.75   $34.70  
  7 purchase totals = $662.06       $706.6319   $706.63   $706.65   $706.50