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 $186.92   9.476%   $204.6325   $204.63   $204.65   $204.60  
  Purchase #2 $167.55   8.176%   $181.2489   $181.25   $181.25   $181.20  
  Purchase #3 $19.80   11.157%   $22.0091   $22.01   $22.00   $22.00  
  Purchase #4 $155.77   6.140%   $165.3343   $165.33   $165.35   $165.30  
  Purchase #5 $237.77   4.636%   $248.793   $248.79   $248.80   $248.80  
  Purchase #6 $117.39   5.548%   $123.9028   $123.90   $123.90   $123.90  
  Purchase #7 $238.75   8.248%   $258.4421   $258.44   $258.45   $258.40  
  7 purchase totals = $1,123.95       $1,204.3627   $1,204.35   $1,204.40   $1,204.20