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 $196.44   10.713%   $217.4846   $217.48   $217.50   $217.50  
  Purchase #2 $151.71   7.745%   $163.4599   $163.46   $163.45   $163.50  
  Purchase #3 $238.93   11.847%   $267.236   $267.24   $267.25   $267.20  
  Purchase #4 $67.88   11.734%   $75.845   $75.85   $75.85   $75.80  
  Purchase #5 $147.91   10.790%   $163.8695   $163.87   $163.85   $163.90  
  Purchase #6 $57.89   4.766%   $60.649   $60.65   $60.65   $60.60  
  Purchase #7 $33.93   11.424%   $37.8062   $37.81   $37.80   $37.80  
  7 purchase totals = $894.69       $986.3502   $986.36   $986.35   $986.30