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 $211.48   10.648%   $233.9984   $234.00   $234.00   $234.00  
  Purchase #2 $150.28   6.630%   $160.2436   $160.24   $160.25   $160.20  
  Purchase #3 $57.34   3.791%   $59.5138   $59.51   $59.50   $59.50  
  Purchase #4 $203.89   6.385%   $216.9084   $216.91   $216.90   $216.90  
  Purchase #5 $239.87   3.774%   $248.9227   $248.92   $248.90   $248.90  
  Purchase #6 $77.97   4.836%   $81.7406   $81.74   $81.75   $81.70  
  Purchase #7 $231.89   12.330%   $260.482   $260.48   $260.50   $260.50  
  7 purchase totals = $1,172.72       $1,261.8095   $1,261.80   $1,261.80   $1,261.70