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 $54.66   3.501%   $56.5736   $56.57   $56.55   $56.60  
  Purchase #2 $46.52   3.546%   $48.1696   $48.17   $48.15   $48.20  
  Purchase #3 $228.86   6.596%   $243.9556   $243.96   $243.95   $244.00  
  Purchase #4 $129.96   13.555%   $147.5761   $147.58   $147.60   $147.60  
  Purchase #5 $64.44   5.739%   $68.1382   $68.14   $68.15   $68.10  
  Purchase #6 $158.26   6.284%   $168.2051   $168.21   $168.20   $168.20  
  Purchase #7 $248.92   5.393%   $262.3443   $262.34   $262.35   $262.30  
  7 purchase totals = $931.62       $994.9625   $994.97   $994.95   $995.00