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 $49.92   11.239%   $55.5305   $55.53   $55.55   $55.50  
  Purchase #2 $210.74   13.462%   $239.1098   $239.11   $239.10   $239.10  
  Purchase #3 $202.36   10.182%   $222.9643   $222.96   $222.95   $223.00  
  Purchase #4 $22.29   8.419%   $24.1666   $24.17   $24.15   $24.20  
  Purchase #5 $156.70   9.244%   $171.1853   $171.19   $171.20   $171.20  
  Purchase #6 $195.73   8.132%   $211.6468   $211.65   $211.65   $211.60  
  Purchase #7 $48.56   5.153%   $51.0623   $51.06   $51.05   $51.10  
  7 purchase totals = $886.30       $975.6656   $975.67   $975.65   $975.70