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 $84.67   13.703%   $96.2723   $96.27   $96.25   $96.30  
  Purchase #2 $5.86   7.590%   $6.3048   $6.30   $6.30   $6.30  
  Purchase #3 $245.96   8.174%   $266.0648   $266.06   $266.05   $266.10  
  Purchase #4 $111.52   10.452%   $123.1761   $123.18   $123.20   $123.20  
  Purchase #5 $246.68   9.792%   $270.8349   $270.83   $270.85   $270.80  
  Purchase #6 $84.53   13.176%   $95.6677   $95.67   $95.65   $95.70  
  Purchase #7 $203.57   10.862%   $225.6818   $225.68   $225.70   $225.70  
  7 purchase totals = $982.79       $1,084.0024   $1,083.99   $1,084.00   $1,084.10