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 $241.86   10.520%   $267.3037   $267.30   $267.30   $267.30  
  Purchase #2 $175.93   4.418%   $183.7026   $183.70   $183.70   $183.70  
  Purchase #3 $207.51   4.263%   $216.3562   $216.36   $216.35   $216.40  
  Purchase #4 $171.26   9.729%   $187.9219   $187.92   $187.90   $187.90  
  Purchase #5 $8.98   10.831%   $9.9526   $9.95   $9.95   $10.00  
  Purchase #6 $30.46   11.766%   $34.0439   $34.04   $34.05   $34.00  
  Purchase #7 $106.41   12.705%   $119.9294   $119.93   $119.95   $119.90  
  7 purchase totals = $942.41       $1,019.2103   $1,019.20   $1,019.20   $1,019.20