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 $85.55   12.542%   $96.2797   $96.28   $96.30   $96.30  
  Purchase #2 $57.50   8.165%   $62.1949   $62.19   $62.20   $62.20  
  Purchase #3 $22.90   4.162%   $23.8531   $23.85   $23.85   $23.90  
  Purchase #4 $205.66   12.203%   $230.7567   $230.76   $230.75   $230.80  
  Purchase #5 $215.78   7.630%   $232.244   $232.24   $232.25   $232.20  
  Purchase #6 $243.93   8.801%   $265.3983   $265.40   $265.40   $265.40  
  Purchase #7 $70.91   9.722%   $77.8039   $77.80   $77.80   $77.80  
  7 purchase totals = $902.23       $988.5306   $988.52   $988.55   $988.60