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 $91.37   10.497%   $100.9611   $100.96   $100.95   $101.00  
  Purchase #2 $111.77   5.156%   $117.5329   $117.53   $117.55   $117.50  
  Purchase #3 $199.28   13.142%   $225.4694   $225.47   $225.45   $225.50  
  Purchase #4 $5.97   12.485%   $6.7154   $6.72   $6.70   $6.70  
  Purchase #5 $229.62   10.601%   $253.962   $253.96   $253.95   $254.00  
  Purchase #6 $173.53   13.116%   $196.2902   $196.29   $196.30   $196.30  
  Purchase #7 $182.27   8.438%   $197.6499   $197.65   $197.65   $197.60  
  7 purchase totals = $993.81       $1,098.5809   $1,098.58   $1,098.55   $1,098.60