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 $225.98   11.741%   $252.5123   $252.51   $252.50   $252.50  
  Purchase #2 $209.46   7.754%   $225.7015   $225.70   $225.70   $225.70  
  Purchase #3 $24.31   8.861%   $26.4641   $26.46   $26.45   $26.50  
  Purchase #4 $131.63   4.344%   $137.348   $137.35   $137.35   $137.30  
  Purchase #5 $188.61   6.715%   $201.2752   $201.28   $201.30   $201.30  
  Purchase #6 $55.53   8.311%   $60.1451   $60.15   $60.15   $60.10  
  Purchase #7 $223.25   10.597%   $246.9078   $246.91   $246.90   $246.90  
  7 purchase totals = $1,058.77       $1,150.3540   $1,150.36   $1,150.35   $1,150.30