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 $248.48   6.104%   $263.6472   $263.65   $263.65   $263.60  
  Purchase #2 $171.33   13.184%   $193.9181   $193.92   $193.90   $193.90  
  Purchase #3 $127.40   5.265%   $134.1076   $134.11   $134.10   $134.10  
  Purchase #4 $174.69   11.687%   $195.106   $195.11   $195.10   $195.10  
  Purchase #5 $38.85   9.456%   $42.5237   $42.52   $42.50   $42.50  
  Purchase #6 $18.93   7.273%   $20.3068   $20.31   $20.30   $20.30  
  Purchase #7 $200.45   5.395%   $211.2643   $211.26   $211.25   $211.30  
  7 purchase totals = $980.13       $1,060.8737   $1,060.88   $1,060.80   $1,060.80