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 $86.91   6.810%   $92.8286   $92.83   $92.85   $92.80  
  Purchase #2 $162.44   10.563%   $179.5985   $179.60   $179.60   $179.60  
  Purchase #3 $24.42   11.245%   $27.166   $27.17   $27.15   $27.20  
  Purchase #4 $233.94   4.265%   $243.9175   $243.92   $243.90   $243.90  
  Purchase #5 $181.52   6.650%   $193.5911   $193.59   $193.60   $193.60  
  Purchase #6 $54.51   4.613%   $57.0245   $57.02   $57.00   $57.00  
  Purchase #7 $13.64   3.756%   $14.1523   $14.15   $14.15   $14.20  
  7 purchase totals = $757.38       $808.2785   $808.28   $808.25   $808.30