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 $169.82   13.849%   $193.3384   $193.34   $193.35   $193.30  
  Purchase #2 $97.60   8.795%   $106.1839   $106.18   $106.20   $106.20  
  Purchase #3 $155.66   8.544%   $168.9596   $168.96   $168.95   $169.00  
  Purchase #4 $29.58   13.414%   $33.5479   $33.55   $33.55   $33.50  
  Purchase #5 $243.44   6.625%   $259.5679   $259.57   $259.55   $259.60  
  Purchase #6 $154.90   6.399%   $164.8121   $164.81   $164.80   $164.80  
  Purchase #7 $113.72   5.372%   $119.829   $119.83   $119.85   $119.80  
  7 purchase totals = $964.72       $1,046.2388   $1,046.24   $1,046.25   $1,046.20