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 $61.83   10.238%   $68.1602   $68.16   $68.15   $68.20  
  Purchase #2 $72.93   10.631%   $80.6832   $80.68   $80.70   $80.70  
  Purchase #3 $200.56   11.826%   $224.2782   $224.28   $224.30   $224.30  
  Purchase #4 $190.59   10.837%   $211.2442   $211.24   $211.25   $211.20  
  Purchase #5 $122.39   5.548%   $129.1802   $129.18   $129.20   $129.20  
  Purchase #6 $235.64   9.304%   $257.5639   $257.56   $257.55   $257.60  
  Purchase #7 $24.97   4.196%   $26.0177   $26.02   $26.00   $26.00  
  7 purchase totals = $908.91       $997.1276   $997.12   $997.15   $997.20