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 $230.61   6.824%   $246.3468   $246.35   $246.35   $246.30  
  Purchase #2 $49.53   12.816%   $55.8778   $55.88   $55.90   $55.90  
  Purchase #3 $64.83   3.202%   $66.9059   $66.91   $66.90   $66.90  
  Purchase #4 $216.86   4.838%   $227.3517   $227.35   $227.35   $227.40  
  Purchase #5 $131.90   11.737%   $147.3811   $147.38   $147.40   $147.40  
  Purchase #6 $120.76   7.290%   $129.5634   $129.56   $129.55   $129.60  
  Purchase #7 $182.85   12.712%   $206.0939   $206.09   $206.10   $206.10  
  7 purchase totals = $997.34       $1,079.5206   $1,079.52   $1,079.55   $1,079.60