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 $82.53   8.442%   $89.4972   $89.50   $89.50   $89.50  
  Purchase #2 $113.66   4.699%   $119.0009   $119.00   $119.00   $119.00  
  Purchase #3 $79.49   7.275%   $85.2729   $85.27   $85.25   $85.30  
  Purchase #4 $98.88   3.562%   $102.4021   $102.40   $102.40   $102.40  
  Purchase #5 $21.83   10.751%   $24.1769   $24.18   $24.20   $24.20  
  Purchase #6 $153.62   11.229%   $170.87   $170.87   $170.85   $170.90  
  Purchase #7 $228.62   5.400%   $240.9655   $240.97   $240.95   $241.00  
  7 purchase totals = $778.63       $832.1855   $832.19   $832.15   $832.30