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 $66.32   10.839%   $73.5084   $73.51   $73.50   $73.50  
  Purchase #2 $65.92   7.566%   $70.9075   $70.91   $70.90   $70.90  
  Purchase #3 $78.55   4.516%   $82.0973   $82.10   $82.10   $82.10  
  Purchase #4 $180.59   8.367%   $195.7   $195.70   $195.70   $195.70  
  Purchase #5 $152.85   9.775%   $167.7911   $167.79   $167.80   $167.80  
  Purchase #6 $142.38   9.732%   $156.2364   $156.24   $156.25   $156.20  
  Purchase #7 $185.29   9.591%   $203.0612   $203.06   $203.05   $203.10  
  7 purchase totals = $871.90       $949.3019   $949.31   $949.30   $949.30