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 $71.56   10.549%   $79.1089   $79.11   $79.10   $79.10  
  Purchase #2 $31.56   7.403%   $33.8964   $33.90   $33.90   $33.90  
  Purchase #3 $243.28   10.814%   $269.5883   $269.59   $269.60   $269.60  
  Purchase #4 $46.72   13.381%   $52.9716   $52.97   $52.95   $53.00  
  Purchase #5 $6.36   4.619%   $6.6538   $6.65   $6.65   $6.70  
  Purchase #6 $167.46   11.193%   $186.2038   $186.20   $186.20   $186.20  
  Purchase #7 $172.93   8.473%   $187.5824   $187.58   $187.60   $187.60  
  7 purchase totals = $739.87       $816.0052   $816.00   $816.00   $816.10