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 $60.71   11.782%   $67.8629   $67.86   $67.85   $67.90  
  Purchase #2 $31.42   4.800%   $32.9282   $32.93   $32.95   $32.90  
  Purchase #3 $10.51   6.692%   $11.2133   $11.21   $11.20   $11.20  
  Purchase #4 $19.97   6.123%   $21.1928   $21.19   $21.20   $21.20  
  Purchase #5 $239.72   12.514%   $269.7186   $269.72   $269.70   $269.70  
  Purchase #6 $62.96   13.715%   $71.595   $71.60   $71.60   $71.60  
  Purchase #7 $208.97   8.148%   $225.9969   $226.00   $226.00   $226.00  
  7 purchase totals = $634.26       $700.5077   $700.51   $700.50   $700.50