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 $188.32   12.566%   $211.9843   $211.98   $212.00   $212.00  
  Purchase #2 $56.99   13.364%   $64.6061   $64.61   $64.60   $64.60  
  Purchase #3 $23.62   11.221%   $26.2704   $26.27   $26.25   $26.30  
  Purchase #4 $87.85   13.207%   $99.4523   $99.45   $99.45   $99.50  
  Purchase #5 $224.82   4.649%   $235.2719   $235.27   $235.25   $235.30  
  Purchase #6 $126.55   12.675%   $142.5902   $142.59   $142.60   $142.60  
  Purchase #7 $13.52   10.852%   $14.9872   $14.99   $15.00   $15.00  
  7 purchase totals = $721.67       $795.1624   $795.16   $795.15   $795.30