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 $163.93   13.582%   $186.195   $186.20   $186.20   $186.20  
  Purchase #2 $235.32   3.408%   $243.3397   $243.34   $243.35   $243.30  
  Purchase #3 $48.99   12.746%   $55.2343   $55.23   $55.25   $55.20  
  Purchase #4 $234.49   4.541%   $245.1382   $245.14   $245.15   $245.10  
  Purchase #5 $155.25   10.223%   $171.1212   $171.12   $171.10   $171.10  
  Purchase #6 $197.98   9.486%   $216.7604   $216.76   $216.75   $216.80  
  Purchase #7 $74.79   5.811%   $79.136   $79.14   $79.15   $79.10  
  7 purchase totals = $1,110.75       $1,196.9248   $1,196.93   $1,196.95   $1,196.80