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 $31.65   13.257%   $35.8458   $35.85   $35.85   $35.80  
  Purchase #2 $172.96   8.197%   $187.1375   $187.14   $187.15   $187.10  
  Purchase #3 $95.42   13.442%   $108.2464   $108.25   $108.25   $108.20  
  Purchase #4 $118.51   4.605%   $123.9674   $123.97   $123.95   $124.00  
  Purchase #5 $183.36   9.801%   $201.3311   $201.33   $201.35   $201.30  
  Purchase #6 $67.77   3.295%   $70.003   $70.00   $70.00   $70.00  
  Purchase #7 $172.54   13.511%   $195.8519   $195.85   $195.85   $195.90  
  7 purchase totals = $842.21       $922.3831   $922.39   $922.40   $922.30