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 $85.52   12.261%   $96.0056   $96.01   $96.00   $96.00  
  Purchase #2 $36.77   11.664%   $41.0589   $41.06   $41.05   $41.10  
  Purchase #3 $58.87   4.762%   $61.6734   $61.67   $61.65   $61.70  
  Purchase #4 $62.45   13.677%   $70.9913   $70.99   $71.00   $71.00  
  Purchase #5 $63.37   9.774%   $69.5638   $69.56   $69.55   $69.60  
  Purchase #6 $163.53   10.540%   $180.7661   $180.77   $180.75   $180.80  
  Purchase #7 $170.56   4.688%   $178.5559   $178.56   $178.55   $178.60  
  7 purchase totals = $641.07       $698.6150   $698.62   $698.55   $698.80