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 $162.45   6.759%   $173.43   $173.43   $173.45   $173.40  
  Purchase #2 $49.86   3.760%   $51.7347   $51.73   $51.75   $51.70  
  Purchase #3 $17.55   8.435%   $19.0303   $19.03   $19.05   $19.00  
  Purchase #4 $208.89   11.610%   $233.1421   $233.14   $233.15   $233.10  
  Purchase #5 $24.82   7.728%   $26.7381   $26.74   $26.75   $26.70  
  Purchase #6 $145.76   10.332%   $160.8199   $160.82   $160.80   $160.80  
  Purchase #7 $185.65   8.582%   $201.5825   $201.58   $201.60   $201.60  
  7 purchase totals = $794.98       $866.4776   $866.47   $866.55   $866.30