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 $205.53   8.506%   $223.0124   $223.01   $223.00   $223.00  
  Purchase #2 $30.85   12.759%   $34.7862   $34.79   $34.80   $34.80  
  Purchase #3 $158.64   12.653%   $178.7127   $178.71   $178.70   $178.70  
  Purchase #4 $95.46   13.458%   $108.307   $108.31   $108.30   $108.30  
  Purchase #5 $174.63   12.853%   $197.0752   $197.08   $197.10   $197.10  
  Purchase #6 $228.74   8.516%   $248.2195   $248.22   $248.20   $248.20  
  Purchase #7 $148.34   5.662%   $156.739   $156.74   $156.75   $156.70  
  7 purchase totals = $1,042.19       $1,146.8520   $1,146.86   $1,146.85   $1,146.80