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 $197.85   3.141%   $204.0645   $204.06   $204.05   $204.10  
  Purchase #2 $248.85   4.662%   $260.4514   $260.45   $260.45   $260.50  
  Purchase #3 $248.47   13.794%   $282.744   $282.74   $282.75   $282.70  
  Purchase #4 $59.72   9.220%   $65.2262   $65.23   $65.25   $65.20  
  Purchase #5 $85.91   7.282%   $92.166   $92.17   $92.15   $92.20  
  Purchase #6 $246.86   9.394%   $270.05   $270.05   $270.05   $270.10  
  Purchase #7 $73.50   13.200%   $83.202   $83.20   $83.20   $83.20  
  7 purchase totals = $1,161.16       $1,257.9041   $1,257.90   $1,257.90   $1,258.00