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 $59.71   12.607%   $67.2376   $67.24   $67.25   $67.20  
  Purchase #2 $145.80   6.387%   $155.1122   $155.11   $155.10   $155.10  
  Purchase #3 $185.78   3.629%   $192.522   $192.52   $192.50   $192.50  
  Purchase #4 $241.37   4.644%   $252.5792   $252.58   $252.60   $252.60  
  Purchase #5 $39.60   10.514%   $43.7635   $43.76   $43.75   $43.80  
  Purchase #6 $104.28   13.543%   $118.4026   $118.40   $118.40   $118.40  
  Purchase #7 $107.79   8.610%   $117.0707   $117.07   $117.05   $117.10  
  7 purchase totals = $884.33       $946.6878   $946.68   $946.65   $946.70