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 $241.74   11.143%   $268.6771   $268.68   $268.70   $268.70  
  Purchase #2 $18.94   7.180%   $20.2999   $20.30   $20.30   $20.30  
  Purchase #3 $81.62   13.581%   $92.7048   $92.70   $92.70   $92.70  
  Purchase #4 $26.82   10.196%   $29.5546   $29.55   $29.55   $29.60  
  Purchase #5 $224.60   10.423%   $248.0101   $248.01   $248.00   $248.00  
  Purchase #6 $230.47   5.833%   $243.9133   $243.91   $243.90   $243.90  
  Purchase #7 $136.34   10.553%   $150.728   $150.73   $150.75   $150.70  
  7 purchase totals = $960.53       $1,053.8878   $1,053.88   $1,053.90   $1,053.90