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 $93.56   3.340%   $96.6849   $96.68   $96.70   $96.70  
  Purchase #2 $193.93   11.666%   $216.5539   $216.55   $216.55   $216.60  
  Purchase #3 $32.93   12.621%   $37.0861   $37.09   $37.10   $37.10  
  Purchase #4 $68.54   5.459%   $72.2816   $72.28   $72.30   $72.30  
  Purchase #5 $234.28   13.257%   $265.3385   $265.34   $265.35   $265.30  
  Purchase #6 $11.84   3.687%   $12.2765   $12.28   $12.30   $12.30  
  Purchase #7 $194.96   13.258%   $220.8078   $220.81   $220.80   $220.80  
  7 purchase totals = $830.04       $921.0293   $921.03   $921.10   $921.10