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 $47.63   10.267%   $52.5202   $52.52   $52.50   $52.50  
  Purchase #2 $165.74   13.127%   $187.4967   $187.50   $187.50   $187.50  
  Purchase #3 $160.57   5.312%   $169.0995   $169.10   $169.10   $169.10  
  Purchase #4 $163.99   5.600%   $173.1734   $173.17   $173.15   $173.20  
  Purchase #5 $154.75   6.526%   $164.849   $164.85   $164.85   $164.80  
  Purchase #6 $85.77   6.763%   $91.5706   $91.57   $91.55   $91.60  
  Purchase #7 $216.59   6.688%   $231.0755   $231.08   $231.10   $231.10  
  7 purchase totals = $995.04       $1,069.7849   $1,069.79   $1,069.75   $1,069.80