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 $55.68   9.560%   $61.003   $61.00   $61.00   $61.00  
  Purchase #2 $20.33   8.762%   $22.1113   $22.11   $22.10   $22.10  
  Purchase #3 $52.57   8.266%   $56.9154   $56.92   $56.90   $56.90  
  Purchase #4 $8.34   6.481%   $8.8805   $8.88   $8.90   $8.90  
  Purchase #5 $84.54   6.142%   $89.7324   $89.73   $89.75   $89.70  
  Purchase #6 $26.33   11.548%   $29.3706   $29.37   $29.35   $29.40  
  Purchase #7 $81.91   12.513%   $92.1594   $92.16   $92.15   $92.20  
  7 purchase totals = $329.70       $360.1726   $360.17   $360.15   $360.20