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 $60.53   10.195%   $66.701   $66.70   $66.70   $66.70  
  Purchase #2 $108.67   13.703%   $123.5611   $123.56   $123.55   $123.60  
  Purchase #3 $230.97   6.862%   $246.8192   $246.82   $246.80   $246.80  
  Purchase #4 $164.43   10.790%   $182.172   $182.17   $182.15   $182.20  
  Purchase #5 $24.93   4.604%   $26.0778   $26.08   $26.10   $26.10  
  Purchase #6 $168.25   13.865%   $191.5779   $191.58   $191.60   $191.60  
  Purchase #7 $115.96   10.324%   $127.9317   $127.93   $127.95   $127.90  
  7 purchase totals = $873.74       $964.8407   $964.84   $964.85   $964.90