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 $182.96   3.159%   $188.7397   $188.74   $188.75   $188.70  
  Purchase #2 $179.93   13.585%   $204.3735   $204.37   $204.35   $204.40  
  Purchase #3 $141.34   10.721%   $156.4931   $156.49   $156.50   $156.50  
  Purchase #4 $24.61   9.268%   $26.8909   $26.89   $26.90   $26.90  
  Purchase #5 $37.67   5.619%   $39.7867   $39.79   $39.80   $39.80  
  Purchase #6 $179.96   13.841%   $204.8683   $204.87   $204.85   $204.90  
  Purchase #7 $175.25   11.577%   $195.5387   $195.54   $195.55   $195.50  
  7 purchase totals = $921.72       $1,016.6909   $1,016.69   $1,016.70   $1,016.70