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 $66.87   3.704%   $69.3469   $69.35   $69.35   $69.30  
  Purchase #2 $208.94   12.445%   $234.9426   $234.94   $234.95   $234.90  
  Purchase #3 $104.43   12.833%   $117.8315   $117.83   $117.85   $117.80  
  Purchase #4 $111.68   7.824%   $120.4178   $120.42   $120.40   $120.40  
  Purchase #5 $90.35   8.215%   $97.7723   $97.77   $97.75   $97.80  
  Purchase #6 $177.29   5.231%   $186.564   $186.56   $186.55   $186.60  
  Purchase #7 $38.62   11.232%   $42.9578   $42.96   $42.95   $43.00  
  7 purchase totals = $798.18       $869.8329   $869.83   $869.80   $869.80