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 $79.51   11.332%   $88.5201   $88.52   $88.50   $88.50  
  Purchase #2 $235.30   3.571%   $243.7026   $243.70   $243.70   $243.70  
  Purchase #3 $53.81   13.812%   $61.2422   $61.24   $61.25   $61.20  
  Purchase #4 $82.95   6.410%   $88.2671   $88.27   $88.25   $88.30  
  Purchase #5 $151.98   6.546%   $161.9286   $161.93   $161.95   $161.90  
  Purchase #6 $75.77   6.365%   $80.5928   $80.59   $80.60   $80.60  
  Purchase #7 $16.91   4.328%   $17.6419   $17.64   $17.65   $17.60  
  7 purchase totals = $696.23       $741.8953   $741.89   $741.90   $741.80