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 $71.64   8.760%   $77.9157   $77.92   $77.90   $77.90  
  Purchase #2 $100.92   3.796%   $104.7509   $104.75   $104.75   $104.80  
  Purchase #3 $156.74   12.243%   $175.9297   $175.93   $175.95   $175.90  
  Purchase #4 $196.55   12.522%   $221.162   $221.16   $221.15   $221.20  
  Purchase #5 $201.75   3.360%   $208.5288   $208.53   $208.55   $208.50  
  Purchase #6 $60.64   9.799%   $66.5821   $66.58   $66.60   $66.60  
  Purchase #7 $183.60   11.631%   $204.9545   $204.95   $204.95   $205.00  
  7 purchase totals = $971.84       $1,059.8237   $1,059.82   $1,059.85   $1,059.90